Li-Ion versus NiMH Batteries

Earth's Independent and Authoritative Source for Digital Camera Battery Information

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Manufacturers of digital cameras, camcorders, cell phones, PDAs, MP3 players, notebook computers, high end bicycle lights, etc., have moved from NiMH to Lithium-Ion batteries for a number of very good reasons. These reasons include weight, size, energy density, cold weather performance, self-discharge rate, and convenience. However there are also some advantages to NiMH AA and AAA batteries.

There are many reasons why one battery type may be better or worse than another. It goes far beyond measuring the number of pictures than can be taken with each type of battery, and it goes beyond being able to buy alkaline AA batteries at 7-11 if your rechargeable batteries run out of juice.

The following advantages of each type of battery are explained in detail further down the page:

* This advantage is over AA batteries in general, not specifically NiMH AA batteries. The advantage applies to AA batteries of other types as well (Alkaline, Lithium, etc.).

* This advantage is over Lithium-Ion batteries in general, and is not an advantage only of NiMH batteries. However this advantage is vastly overstated since alkaline batteries are only good for 10-20 photos.

Battery Basics Understanding the Difference Between Volts, Milliamps, Watts, & Watt Hours

Until I read a post in a Usenet forum on digital photography (rec.photo.digital), I didn't realize that some people are very confused between mAH and WH. This misunderstanding led to some bizarre (and incorrect) conclusions. Here is some basic information about batteries that is essential to understand.

Energy is not measured in milliamp hours (mAH) or watts (W); it's measured in watt-hours WH (at least batteries typically use the watt-hour unit).
The mAH rating of a cell or pack tells you nothing without knowing the voltage of the cell or pack.
Comparing mAH ratings of batteries is meaningless. What matters is the amount of energy stored in the battery, commonly measured in WH (watt hours).
To determine the WH rating of a battery, multiply the voltage in volts by the milliamp hour rating in mAH, and divide by 1000.
If comparing batteries of the same voltage, then the mAH rating does determine which battery stores more energy.

Example

One 7.4V, 2000mAH, lithium-ion battery pack stores 14.8WH of energy (7.4V * 2000mAH / 1000). This is a typical after-market BP511 battery pack used in many Canon digital SLRs (and some older point & shoot cameras).
Four 1.2V, 2000mAH, NiMH AA cell stores 9.6WH of energy (1.2V * 4 * 2000mAH / 1000). Many super-zoom point and shoot cameras use four AA cells. The low self-discharge Sanyo Eneloop cells are rated at 2000mAH.

As you can see, both the lithium-ion battery pack and the NiMH AA cell are rated at 2000mAH. Some people look only at the mAH ratings and conclude that a $10 four-pack of low self-discharge NiMH cells is cheaper than a $12 lithium-ion battery pack. In fact, the Li-Ion pack has a lower cost per unit of energy stored.

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Some people are philosophically opposed to Li-Ion battery packs because of their proprietary nature. Camera manufacturers have traditionally charged high prices for extra battery packs, and it isn't possible to substitute alkaline AA batteries for a Li-Ion pack if your batteries go dead in the middle of nowhere*.

On the other hand, Li-Ion battery packs have a number of technical advantages over NiMH batteries, including a much lower self-discharge rate, greater energy density (in terms of both weight and volume), far better low-temperature performance, a greater maximum number of charge/discharge cycles, and the ability for the camera to provide a fairly accurate indication of remaining capacity. This is why virtually every new digital SLR, and virtually every high end digital camera, uses Li-Ion battery packs. It's also why notebook computers, PDAs, cell phones, MP3 players, etc., use Li-Ion battery packs. After-market Li-Ion battery packs are available at very good prices, in fact if you look at the big picture and compute the total cost including accounting for the number of charge cycles, Li-Ion batteries are often less expensive. Now even some high-end rechargeable bicycle lights and flashlights are using Li-Ion batteries.

*For digital SLRs, A vertical grip that can use AA batteries is a good compromise, offering both the advantages of Li-Ion, and the emergency availability of AA cells. Canon has battery grips available for all of their digital SLRs that don't have integrated vertical grip. There are no vertical grips that take AA batteries for the Nikon D50 or D70/D70s (there is an after-market vertical grip for the D70/D70s but it takes only Li-Ion battery packs).

Heavy users of NiMH batteries (other than eneloop and its variants) are often forced into becoming what's known as a "Battery Hobbyist." A battery hobbyist spends an inordinate amount of time worrying about their batteries. They buy elaborate chargers that allow them to condition (and recondition) their NiMH cells. The same chargers are used to measure the capacity of each cell so they can match capacities within a set. They devise clever methods to mark each sell in a set. They devise rotation systems for the sets to keep them charged when not in use. They build trickle chargers that enable them to keep large numbers of cells topped up. It's a lot of aggravation to keep their devices powered, and to keep spare sets of batteries at the ready. I admit it, I was a battery hobbyist once! I still use a lot of NiMH batteries, but I am slowly moving to all Sanyo eneloop which is a lot less aggravation.

One reason the manufacturers of high-end devices, including cameras, moved to Li-Ion and Li-Po battery packs is that these types of batteries greatly reduce the aggravation level. Consumers will buy more product when they are not forced to spend an inordinate amount of time on maintaining the product in a ready to use condition.

Some people believe that Li-Ion batteries are some sort of an elaborate scam or conspiracy by the camera manufacturers, notebook computer manufacturers, cell phone manufacturers, PDA manufacturers, etc., to extort money out of consumers from the eventual sale of spare battery packs. This is untrue. As an engineer I have worked extensively with many of the top manufacturers of portable devices, in Japan, Taiwan, and Korea, as well as in the U.S.. There are many considerations that a manufacturer must make in terms of battery selection when designing a product. The biggest issues are, size, weight, capacity, battery characteristics, and battery management. The possibility that the owner of a device, might, at some time in the future, buy a spare battery pack from the manufacturer, is an absolute non-issue in the design process. In fact, the reason that the lower-end products use AA batteries, as opposed to Li-Ion, is a marketing decision which is made to save the manufacturer the expense of providing a battery and charger with the device (some AA powered cameras do include a charger and batteries, but most don't). Furthermore, the manufacturer knows that if the product is successful that there will soon be after-market battery packs for their products available at lower cost, and that this will further help sales of their product. Except for a few devices with non-user replaceable batteries (iPhone, iPod, iPad, etc) the manufacturer is not expecting to make lots of money selling battery packs.

There are a couple of individuals that spread misinformation about batteries on various on-line forums and Usenet newsgroups, in an effort to promote their own personal agenda. One of the purposes of this web site is to counter all the junk science being promulgated in forums such as rec.photo.digital.

USB charging works okay for things like phones, where the 3.7V Li-Ion batteries are usually well under 1000mAH. A 3.7V battery is close to ideal for charging from a 5V source, and you don't have to do any DC-DC conversion, you basically control the current and monitor the temperature. But to charge two 2900mAH AA batteries from a 500mA USB port would take longer than many people are willing to tolerate.

Do the math, but don't make the non-techie mistake of looking only at the 500mA USB current, you have to look at both current and voltage, as well as conversion losses and charging losses. Two 2900mAH 1.2V AA cells provide about 7000mWH. A USB port can provide 2500mW. Unfortunately the charge time isn't 7000mWH/2500mW=2.8 hours, there are losses in the voltage conversion from 5V to 3V, so you'll end up with about 3V/750mA. There are additional losses in charging NiMH batteries, it takes about 150% more power to charge a battery than you get out, the rest is lost as heat. So it takes about 150% x 7000mWH = 10500mWH to fully charge two 2500mAH 1,2V AA cells. 10500mWH/(3V x 750mA)=4.7 hours.

Of course since you usually won't be charging them from fully discharged, the time will be more like 3-4 hours, so it might be acceptable, but nothing like the present fast chargers. Since the "charge one battery while using the other battery" system seems to be desirable for digital cameras, there's no rush by camera manufacturers to add several dollars of cost for a feature that few people care about. With USB 3.0's higher current (900 mA), it becomes more practical to use the USB port as a power port. There is also a USB specification for charging which specifies a charging current of up to 1.5A (see http://www.usb.org/developers/devclass_docs/batt_charging_1_1.zip) but this assumes a dedicated charger able to provide this much current, not the standard USB port on a desktop or notebook PC.

The situation is a bit better for 3.7V Li-Ion batteries. A 2000mAH 3.7V Li-Ion battery provides 7400mWH of energy. Since you can charge directly from 5V there are no conversion losses, and Li-Ion charging is more efficient, requiring only about 125% more power to charge the battery than you get out.

Almost no standard AA powered cameras have internal charging capability from either USB or a proprietary charger (actually I don't know of a single one!). The manufacturer would rather not spend anything extra for internal charging circuitry, as well as the circuitry to detect a rechargeable NiMH cell versus a lithium or alkaline cell, and be responsible for any problems. There have been some li-ion powered cameras with in-camera charging (i.e. the early Canon G series cameras), but it did not catch on. Some Kodak cameras used a proprietary NiMH battery pack and could do internal charging.

Nearly every current digital SLR on the market uses Li-Ion battery packs, with the exception being models from Pentax/Samsung. Looking only at the size issue, it would seem that digital SLRs would be a good fit for AA batteries since the size constraints are not as severe as with compact and ultra-compact models. However there are compelling reasons why digital SLRs are especially ill-suited to AA batteries, including energy density, usage patterns, reliability, gauging, and the power consumption of more powerful built in flash units and the power consumption of the larger motorized lenses.

Unless you are leveraging a large collection of compatible lenses, avoid any digital SLR that does not use Li-Ion battery packs in the body. In order to use Li-Ion packs on a Pentax, you must purchase an after-market vertical grip which enables the camera to use a wide variety of Li-Ion battery packs, or twelve AA batteries. While the vertical grip is a great accessory, it's not something that you probably want to leave attached to the camera all the time.

Many Li-Ion powered digital SLRs can use AA batteries in the optional vertical grip attachment. This is a good solution for those that feel more comfortable when it is possible to use AA batteries in a pinch. Vertical grips are such a popular accessory that even when the camera manufacturer doesn't have the resources to develop one, the after-market is quick to step in and fill the demand. The AA batteries are inserted into a tray which slides into the grip. This eliminates one of the major drawbacks of AA batteries, where the fragile battery door is part of the circuit.

"One of the biggest complaints I hear from occasional digicam users is in regards to the NiMH batteries being dead or near-dead when they go to use the camera. NiMH type batteries are wonderful if freshly charged, when sitting idle however they are subject to a hefty air-discharge rate. Lithium battery technology also suffers from a certain amount of air-discharge but nowhere near as great as that of NiMH. " Steve's Digicams

Li-Ion and Li-Polymer batteries have a self-discharge rate of between 1-3% per month (when installed in a device, the self-discharge rate may be a little higher). If you look at one of the application notes from Maxim at http://www.maxim-ic.com/app-notes/index.mvp/id/3958 they have the following table (which does not include the new low self-discharge NiMH batteries like the eneloop):

Regular NiMH batteries have a self-discharge rate of between 30-50% per month. For devices that are used only occasionally, NiMH batteries are not a good choice, unless the device is always plugged in when not in use. The graph below shows the self-discharge rates of Li-Ion, NiCad, and NiMH batteries. I have used best case data for NiMH and NiCad batteries, and worst case data for Li-Ion batteries. Note that this data is for batteries where the device is not putting any load on the battery when the device is off, or for where the battery is removed from the device. The new Sanyo eneloop NiMH batteries solve the self-discharge problem for NiMH batteries, and are now available at reasonable prices (Amazon charges $19.99 for eight cells including shipping if your order is over $25 while Thomas Distributing charges $13 for four cells not including shipping). See http://www.eneloop.info/ for information about Sanyo's new eneloop NiMH batteries. Another version of these batteries is the Hybrio; Amazon charges $14.12 four cells including shipping if your order is over $25. The Hybrio is slightly higher capacity. See http://www.users.on.net/~mhains/Reviews.html for a good analysis of different NiMH batteries.

Unless you need the highest possible capacity AA rechargeable batteries, stick with the eneloop cells. At $2.50 each they are only slightly more expensive than the high self-discharge NiMH batteries, though they are of lower capacity.

"A major contributor to high self-discharge on nickel and lead-based batteries is a high cycle count and/or old age. With increased cycles, the battery plates tend to swell. Once enlarged, the plates press more firmly against the delicate separator, resulting in increased self-discharge. This is common in aging NiCd and NiMH batteries but can also be seen in lead acid systems. Loading less active materials on the plates can reduce the plate swelling on nickel-based batteries. This improves expansion and contraction while charging and discharging. In addition, the load characteristic is enhanced and the cycle life prolonged. The downside is lower capacity. Metallic dendrites penetrating into the separator are another cause of high self-discharge. The dendrites are the result of crystalline formation, also known as memory. Once marred, the damage is permanent. Poorly designed chargers that ‘cook’ the batteries also increase the self-discharge. High cell temperature causes irreversible damage to the separator."

Sanyo eneloop

Sanyo's eneloop batteries have essentially solved the high self-discharge problem of NiMH batteries, with the side benefit of an increased number of charge/discharge cycles (Sanyo claims 1000 cycles).

The technology used by Sanyo is as follows (according to marketing literature)

The cathode (negative electrode) is constructed from a "new super lattice alloy" that reduces its chemical decomposition

The anode (positive electrode) uses a new material that slows its separation

The separator material was changed to slow its decomposition

The electrolyte was "improved"

"Sanyo Energy Twicell brought together and used previous technological developments in their development of a material that would control the self-discharge induction mode, development of a new-composition, super-lattice hydrogen absorbing alloy, and optimization of the composition of electrolyte solution, registering several patents in the process."

While the eneloop, and other low self-discharge cells, solve one of the major problems with NiMH cells, they still have most of the drawbacks of AA cells in general, and NiMH cells in particular.

NiCad batteries are by far the best in terms of the maximum number of charge/discharge cycles. Next are Li-Ion and Li-Polymer, then NiMH (early Li-Po batteries had a life of only about 250 cycles, but they have been improved in the past couple of years). Be sure to take the number of charge/discharge cycles into account when comparing battery costs, because the Li-Ion battery pack can have up to twice as many charge/recharge cycles as NiMH batteries. Furthermore, the Li-Ion battery pack needs to be charged less often due to its higher capacity, and due to its much lower self-discharge rate. Sanyo's eneloop NiMH batteries claim 1000 charge/discharge cycles, plus due to their low self-discharge rate, they will need to charged less often than regular NiMH batteries.

Remember that the claimed maximum number of charge/discharge cycles for NiMH batteries are wildly optimistic. Paul Rubin, a frequent contributor to rec.photo.digital, wrote: "I've never seen a NiMH battery last anywhere near the vendor's claims of 300-500 charge cycles. 150 or so is the best I've seen despite a fairly careful charge/discharge regimen." Many users will easily reach the actual limit of charge cycles.

Another consideration is the fact that NiMH batteries perform best with full charge/full discharge cycles. This does not fit the typical usage pattern of devices such as digital cameras, PDAs, and cellular phones. An article in Portable Design magazine states:

NiMH, which is lower cost than Li-Ion, can make sense when the product's normal use pattern is not unhealthy for the cells. This consideration is particularly important in low-cost products that are unlikely to include sophisticated charging since NiMH cells prefer full charge/discharge cycles. This is suitable for products that are frequently used to exhaustion, such as power tools.

Another pattern that fits NiMH is as alkaline "replacements," where cells are removed from the device when depleted, but then charged in an external charger. This is common in digital cameras, but requires a lot of attention from the consumer.

Many portable information products do not conveniently fit this pattern. PDAs and cell phones are charged regularly but drained sporadically. These products need Lithium-Ion batteries. In addition to their power-to-weight ratio, these batteries provide two more important advantages: low self-discharge and no difficulty with small charge-discharge cycles. Consumers thus devote little effort to "battery management" and instead simply use the product and rarely think about the batteries.

However, the Li-On battery does have a shorter useful life, in terms of time, than NiMH batteries. A Li-Ion rechargeable battery will last about three years, starting from the time of manufacture, versus about five years for a NiMH battery. Unless you're a professional photographer, It's likely that you'll never reach the maximum number of charge/discharge cycles, before the three years is up, and the Li-Ion battery begins losing capacity. There are ways to extend the life of Li-Ion batteries, specifically by storing them in a cold place (but never freezing them).

Lithium Polymer (Li-Po) batteries have about half the number of charge/discharge cycles as Li-Ion batteries. The advantage of Li-Po batteries is that they can be charged at a much higher rate.

Li-Ion batteries last longest when the battery is partially discharged the fully charged. This is how devices such as cell phones and digital cameras are normally used, with the battery rarely completely run down. NiMH batteries last longer, and retain more capacity, if the battery is fully discharged prior to being charged. There are some high-end NiMH chargers that can completely discharge the batteries prior to charging. Unfortunately, one of the modes on the Maha MH-C9000 is not "completely discharge then charge," you must manually initiate a charge cycle following discharge. The LaCrosse BC-900 does have a mode to completely discharge the battery, then initiate charging, without any user intervention. Most NiMH chargers have no capability to completely discharge the battery prior to recharging.

The proper charging regimen for NiMH batteries is very complicated, and is detailed in the section Care and Feeding of NiMH Batteries.

Li-Ion batteries have a self-discharge rate that remains constant during the life of the battery, regardless of the cycle count. NiMH batteries, including the new eneloop and Hybrio cells, have a steadily increasing level of self-discharge as the cycle count increases.

"High cycle count and aging has little effect on self-discharge on lithium-based batteries."

"NiCad and NiMH battery chemistries exhibit a high level of self-discharge. If left on the shelf, a new NiCd loses about 10 percent of its capacity in the first 24 hours after being removed from the charger. The rate of self-discharge settles to about 10 percent per month afterwards. At a higher temperature, the self-discharge rate increases substantially. As a rule, the rate of self-discharge doubles with every 10°C (18°F) increase in temperature. The self-discharge of the NiMH is about 30 percent higher than that of the NiCd.. A major contributor to high self-discharge on nickel and lead-based batteries is a high cycle count and/or old age. With increased cycles, the battery plates tend to swell. Once enlarged, the plates press more firmly against the delicate separator, resulting in increased self-discharge."

A major problem with Li-Ion cells is that cells begin to permanently lose capacity as soon as they are manufactured. According to http://www.maxim-ic.com/app-notes/index.mvp/id/3958 , fully charged cells lose 20% of their capacity per year, while partially (40%) charged cells lose only about 4% of their capacity per year. Of course the end-user of a digital camera is not going to want to keep spare batteries around that are only charged to 40%.

Weight
Li-Ion batteries have a much higher energy density. This means that you can fit the same energy into a smaller space, or more energy into the same size space. Similarly the equivalent capacity NiMH and Li-Ion battery packs will have a weight difference of between 2 to 1 and 4 to 1, with the Li-Ion being lighter. The chart below shows the relative energy densities, by weight, of NiCad, NiMH, Sanyo eneloop, Li-Ion, and Li-Polymer batteries. Note that the Sanyo eneloop batteries now available have a rating of 2000mAH for the AA cells, but this is expected to improve over time, to a level equal to standard NiMH batteries.

Example with latest NiMH and Li-Ion batteries (assuming no weight increase of either):

Volume
The chart below shows relative energy densities, in terms of volume, of NiCad, NiMH, Sanyo eneloop, and Li-Ion batteries (with Li-Ion at 100% and other batteries benchmarked against Li-Ion). I have used 2500mAH NiMH AA cells for the NiMH source data. Earlier NiMH cells were only about 30% more energy dense than NiCad cells, but with continuing improvements in NiMH capacity, they are now about 65% more dense than the highest capacity NiCad cells. This chart is for volume, not for weight. NiMH cells are about 30% heavier than NiCad cells of the same size, but can be as much as four times as dense as NiCad batteries in terms of volume. Note that the Sanyo eneloop batteries now available have a rating of 2000mAH for the AA cells, but this is expected to improve over time, to a level equal to standard NiMH batteries.

Example with latest NiMH and Li-Ion batteries (assuming no weight increase):

If the AA cells were 3000 mAH, and the Li-Ion was 2000mAH, then they would be about equal in energy density by volume. The volume advantage of Li-Ion is small, and declining, at least for camera batteries. For larger batteries, using prismatic cells, lithium based batteries still have a big advantage. The volume calculations assume zero space between the AA cells, which of course is not the case in reality.

It is very rare to find an ultra-compact camera that uses AA batteries, due to the size issue. In fact the only one that barely qualifies is the Samsung Digimax S500.

It is much easier to swap a single battery pack than to fumble with a bunch of individual batteries. It is much more convenient to snap a single battery pack into a charger than it is to insert individual cells. It is much easier to keep track of a battery packs, than to keep track of multiple sets of AA cells, though various devices and marking systems are available to ease this task. Li-Ion battery packs are keyed to prevent insertion incorrectly (with reverse polarity). AA batteries are easily inserted incorrectly, especially by non-technically astute users, children, and the elderly.

Many digital SLRs can use six AA batteries in the optional vertical battery grip (or two Li-Ion packs). Six or eight AA batteries go into a tray which is inserted into the grip. This solves the problem of fumbling with twelve AA batteries, since they sell spare trays (as well as solving the problem of flaky battery doors).

As a poster on rec.photo.digital write: "No way do I want to mess with fiddly AA cells rolling all over the place - eight hanging around ready to be lost at some critical moment, with no easy way of telling if they belong to the charged set or the exhausted set! I want Li-ion!" and "...managing four or eight cells, potentially rolling round all over the place, is not as convenient as having two rectangular batteries. You also need to be careful to remember which of the eight are charged, and which discharged. They may also be bulkier and heavier, increasing camera size and weight."

Non-Replaceable Li-Ion and Li-Polymer Batteries

One big exception to rechargeable Li-Ion (and Li-Polymer) batteries being a good choice is when they are non-replaceable. There do not appear to be any cameras that have gone this route, but it's conceivable that a small low end camera may go this route eventually, in order to keep the camera very thin and to save money in manufacturing.

Many MP3 players have sealed batteries. For example, Apple has chosen to seal the batteries inside the iPod, and charges $59 to replace a battery. However, the after-market has responded quickly, and offers replacement batteries, tools to open the iPod, and even a video that demonstrates how to do the battery replacement. After-market batteries are $25-30.

You don't have much choice if you want a disk based MP3 player, or an iPod Mini or iPod Nano--these all have integrated batteries in a sealed case because it would be very difficult to keep them that thin with an easily replaceable battery pack. However, there are many small MP3 players that run off of a single AAA battery.

* This advantage is over AA batteries in general, not specifically NiMH AA batteries. The advantage applies to AA batteries of other types as well (Alkaline, Lithium, etc.).

"At low temperatures, battery performance may be reduced and the low battery icon may appear earlier than usual. Under
these conditions, restore battery performance by warming it in a pocket immediately before use." Canon A630 manual

Low temperatures slow down the energy conversion in batteries. Different chemistries are affected differently by temperature. NiMH batteries have very poor cold-temperature performance, while Li-Ion batteries have very good low-temperature performance. Ironically, Ni-Cad batteries have better low-temperature performance than NiMH batteries. See See: http://www.urbanfox.tv/articles/batteries/b1batteries.html and http://www.facilitiesnet.com/ms/article.asp?id=3001 for more details. Digital cameras are often used outdoors, in cold weather, so NiMH batteries should be avoided if you expect to use your camera in cold conditions. You can use disposal AA lithium cells in AA powered cameras, in cold weather. You can use AA NiCad cells, though these are no longer widely available, so you'll probably have to order them on-line (see http://www.batterywholesale.com/battery-store/proddetail.html?prodID=1294. If you go the NiCad route, be sure that your battery charger is designed to charge NiCad cells as well as NiMH cells. Remember that NiCad AA cells are about 1/3 the capacity of NiMH AA cells.

If you have an AA powered camera, check to see if it can use RCR-V3 batteries in place of two AA cells. These are rechargeable Li-Ion battery packs that are the size of two AA cells. Many AA powered cameras can use them, but it depends on the battery compartment dimensions. See http://www.delkin.com/pdf/product_docs/rcr_v3.pdf for more details. The down side of these batteries is that they are about four times as expensive as a Li-Ion battery pack (you need two of them for a camera powered by four AA batteries), and you'll need two chargers to charge a set of them at once.

Here are discharge graphs, over temperature. The data is taken from battery manufacturer data sheets, and is only as accurate as what the battery manufacturers publish. The Li-Ion battery loses only about 12% of its capacity at -20 degrees Celsius, compared to about 80% for the NiMH battery. The NiCad batteries actually do much better than the NiMH cell with a loss of about 50%.

There is no temperature data available on Sanyo eneloop batteries. They should be about the same as regular NiMH batteries.

The more battery contacts in a device, the less reliable it is. Battery contacts get dirty. Spring loaded contacts suffer from metal fatigue. Plastic battery doors that must put pressure against the batteries in order for the batteries to make contact, eventually break. There are literally thousands of complaints about the plastic battery doors breaking on digital cameras that use AA batteries. Basically what happens is that the constant pressure of the AA batteries eventually breaks the little plastic tabs on the battery door, or the tabs break if the camera is not handled gently. On Li-Ion equipped digital cameras, the battery door is not usually used to hold the battery against the battery contacts, and even if the door breaks the camera still functions normally. The battery door issue is actually a very serious issue, one that is constantly brought up in various forums. Even if under warranty, it's a big hassle to get it replaced, and often the manufacturer will claim abuse and not cover the repair.

Note that the reliability problems are not caused by the AA batteries, but by the poor design of most cameras that use them

I put in this statement because one individual on rec.photo.digital mistakenly believed that I was blaming the AA batteries for the reliability problems with the cameras that use them. I'm not. It would certainly be possible to design a very reliable battery door. In fact some people have even designed and fabricated devices to hold doors with broken tabs in place, see http://nikon-repair.stonepics.com/nikon_battery_door_repair.htm. You could do this for many other cameras as well, given the desire. The point I am making is that on most Li-Ion powered cameras the battery door is there just to cover the battery pack, it doesn't hold the pack in place, nor is it part of the power circuit.

"I've had my Nikon Coolpix 3100 for a bit more than two years....I was quite happy with this digital camera. Was? Yes, was. The battery door locker has broken. This tiny piece of plastic moulded with the body of the camera was bound to break the way it's build. I've send an email to Nikon France and was not impressed by the answer. "Send us the camera, we will make you a repair proposal, if you refuse this proposal it will cost you € 25.08 w/o VAT". How customer friendly ! So I'm the only person on earth that has had this battery door problem ? I don't think so if you have a look at users forums! Seems to affect a large number of their different models too."

"On the other hand, the major failure of this camera lies in a poorly designed and cheaply built battery door. Nikon's chief battery door designer was apparently sick that day, and the janitor obviously submitted the design they used. Eventually, even if you're careful, the chintzy little lightweight plastic slots on the camera body that the battery door tabs lock into, will break, and your otherwise finely made and great performing camera will need a generous strip of duct tape to hold the door closed - this makes the necessity of using the highest capacity NiMH battery you can find all that more important."

"The batteries sit underneath a rather flimsy hinged door that has a rather annoying habit of pinging open at the slightest knock (there is no lock). More than once I found myself scrambling on the floor attempting to retrieve the batteries after the door had 'popped'. Stupid, stupid design."

Replacement battery doors for many cameras are available from http://www.digitalcamerapartsdepot.com/. However be sure that the damage isn't flimsy plastic tabs inside the camera, rather than tabs on the door itself. If the tabs that break are inside the camera, buy a roll of duct tape. The problem is so widespread there is even development going on in after-market door repair solutions. For example, http://nikon-repair.stonepics.com/nikon_battery_door_repair.htm offers a door repair solution for the Nikon CoolPix 990 and 3100 models (you may be able to fabricate something similar if the camera has a tripod mount and if the battery door is on the bottom).

It's been pointed out that this reliability issue is not related to the actual battery chemistry and this is a true statement However it's a major side effect of the type of battery. Most of us have run into this type of issue on battery powered devices, whether it's on an expensive camera, or on a cheap flashlight. On some NiMH and Ni-Cad powered devices, the batteries are in packs, and have solder-tabs rather than pressure contacts, but you're back to the issue of proprietary battery packs.

Many digital SLRs can use six AA batteries in the optional vertical battery grip (or two Li-Ion packs). The six AA batteries go into a tray which is inserted into the grip. This solves the problem of flaky battery doors (as well as the problem of fumbling with twelve AA batteries, since they sell spare trays).

* This advantage is over AA batteries in general, not specifically NiMH AA batteries. The advantage applies to AA batteries of other types as well (Alkaline, Lithium, etc.).

Many electronic devices draw a small amount of power from the battery, even when the device is off. Leaving NiMH batteries inside such a device, for an extended period of time, will damage the batteries. Usually the weakest cell will be damaged, while the other cell (or cells) will be able to be recharged. Do not leave NiMH batteries inside a device that is used infrequently (less than every couple of months).

For the most part, only lower end digital cameras use AA batteries. The manufacturer does this do save cost, since they do not have to supply a rechargeable Li-Ion battery with the camera. Of course for camcorders, cellular phones, PDAs, etc., there are no longer many devices using NiMH batteries, so you have no choice but to go the Li-Ion route.

For example, let's look at the most popular digital SLR cameras (at the time I wrote this), the Canon EOS-350D, Canon EOS-20D, Nikon D50, and the Nikon D70s. All use Li-Ion battery packs. The Canon cameras can use AA cells with the optional battery grips (or two extra Li-Ion packs can be used in the battery grip). Look at the higher end compact digital cameras, and almost all of them use Li-Ion battery packs.

Now let's look at two somewhat similar 7 megapixel cameras from Canon, the G6 and the A620. The two are similar, but the G6 has several advantages besides the included Li-Ion battery pack. These advantages include a better lens, a remote control, a hot shoe for an external flash attachment, Compact Flash memory instead of SD memory, RAW option, and better software. Of course the G6 also costs nearly $200 more than the A620, but it's a much better, and more versatile camera, for those that are more serious about photography.

The Canon A series is a very good line of inexpensive cameras, and the type of battery it uses is a relatively minor consideration. However some people have become fixated on AA batteries, and refuse to look at any camera that uses a Li-Ion battery. This is a shame, especially if they are interested enough in photography to move up a level in terms of the capability of their equipment.

Some more specialized cameras are only available with Li-Ion rechargeable batteries. For example, the waterproof cameras from Olympus and Pentax all use Li-Ion batteries. Since this type of camera is more likely to be used on extended trips away from a charger, no doubt the manufacturer wanted to make it as convenient as possible to carry spare batteries with a minimum of extra weight and volume.

Ni-Cad, NiMH, and Li-Ion batteries are capable of delivering very high amounts of current. Li-Ion packs are constructed with protection circuitry to guard against shorts, which could cause fire or explosion. Inside each pack is a small printed circuit board with charging and protection circuitry. Ni-Cad and NiMH cells do not have charging or protection circuitry, relying on the device or the charger for charging control and protection.

Note that buying name-brand Li-Ion battery packs does not guarantee anything. There are often recalls of name-brand Li-Ion battery packs.

"SOC—Because of a strong correlation between SOC and OCV for particular Li-ion battery chemistry, the SOC can be estimated from the OCV of the battery. The OCV I <sic> measured when the cells are in relaxation mode, which is defined as the state of the battery when its current is below a small threshold (such as 10mA) and when the cell voltage is stabilized." From http://www.eetasia.com/ART_8800508929_765245_NT_7bef2305.HTM.

One very useful feature of most Li-Ion powered cameras is a reasonably accurate charge level indicator. This is possible because the voltage of a Li-Ion battery is almost linearly related to the remaining capacity. This is not the case for NiMH batteries which have a flat discharge curve until just before they run out. To implement accurate battery capacity measurement on AA powered cameras would add significant manufacturing cost ($1-2) for a feature that is not marketable (megapixels and LCD screen size are what's marketable!). Such measurements on AA powered cameras are further complicated by the need to measure different chemistries of AA batteries, including NiMH, lithium, and alkaline, all of which have significantly different characteristics. This issue is not limited just to cameras. Users have reported problems on devices such as portable GPS units, where the battery gauge is designed for the linear discharge curve of alkaline batteries.

While coulomb counting (keeping track of coulombs-in (during charging) and coulombs-out (during discharging), combined with voltage and temperature monitoring (along with keeping track of charge cycles and age) is preferred for the most accurate gauging, this is not done in most camera batteries because of the cost. It's done in consumer products like the iPhone which uses a smart fuel gauge chip. Some digital SLRs now have smart batteries that do coulomb counting, but it raises the cost of the replacement batteries. For example the Nikon EN-EL3E battery (used in the D200) has a smart-battery chip and some flash memory in the battery. After-market replacements are around $18.50, versus $10 for the older EN-EL3 battery (prices from SterlingTek).

The MB-D200 vertical grip for the Nikon D200 can take six AA batteries or two EN-EL3E batteries. In order to ensure a more accurate battery level indicator, there is a way to tell the camera which type of batteries you are using, Li-Ion, or one of four types of AA batteries (all of which have different characteristics). While a good D-SLR like the D200 makes the effort to gauge NiMH charge capacity as accurately as possible. the problem with NiMH cells is that the voltage difference between 90% charged and 20% is nearly flat. You need a set of very accurate voltage references to use with comparators and A/D converters to accurately gauge NiMH and the other types of AA batteries that can be used in the cameras that use AA batteries. That's not going to happen in a $100 camera. Even the Canon SX20IS, probably the best super-zoom on the market today, does not have a way to set the type of AA battery being used. If you install CHDK then you can set some voltage thresholds which give you more information on the state of charge, but it's still dependent on voltage.

Digital cameras with Li-Ion batteries provide a fairly accurate indication of the level of charge. This is because the voltage of Li-Ion batteries declines fairly linearly between full charge and 90% discharged. Even measuring to only 0.2 volts will give a very good indication of remaining capacity. The curve will be about the same for disposable lithium AA cells.

Voltage Versus Capacity of a 2000mAH 7.4V (two cell) Li-Ion
Battery Pack at 30 Degrees Centigrade and 0.7C Discharge Rate

Lithium polymer cells have a linear discharge curve, but within a much narrower range of voltages than a lithium-ion battery, about a 1 volt range from full capacity to empty. This is still a much greater range than NiMH batteries, so fuel gauges are not difficult to implement. Li-Po batteries have become popular in high end radio-controlled toys such as airplanes, as well as in cellular phones (the Apple iPhone uses a Li-Po battery. While the Li-Po resistance per cell is higher than Ni-Cad resistance, you need more Ni-Cad batteries in series to achieve the same capacity, so the Li-Po internal resistance is actually less. Note that a fully charged two-cell Li-Po battery pack has a voltage level of about 8.4V, versus about 7.8V for a Li-Ion battery pack.

NOTE: The top voltage is for a fully charged battery, not under load. When under load, a fully charged battery will quickly fall to the rated voltage of 3.7 volts per cell.

A NiMH cell has a very narrow output voltage range until it is almost fully discharged. As the article Gas Gauging Enhanced by Current Monitors states: "Unfortunately, for many cell technologies, the cell voltage continually changes during discharge and is very dependent on the temperature of the cell, the rate of discharge and the temperature at which the cell was charged. The greatest changes in cell voltages occur at the beginning and the very end of cell discharge.¹" The graph below has the same scale as the graph for the li-ion battery in the chart above. As you can see, most of the capacity of the NiMH cells (graph is for four cells in series) is in a narrow voltage range of 4.6 to 4.8V, a voltage change of only 0.2V, while the Li-Ion pack is almost linear for voltage versus capacity over a 2V range. Even if the camera manufacturer put in a very accurate voltage measurement circuit on AA powered cameras, they'd also need to have a look-up table that converted voltage to capacity, since the relationship is so non-linear. They'd also need a switch that let the user indicate whether they were using NiMH, Alkaline, or Lithium AA cells, since the voltage versus capacity characteristics are so different between different chemistries (Nikon has such a switch on the battery grip of some of their digital SLRs). To make a long story short, instead of an accurate capacity gauge, most AA powered cameras simply indicate when the batteries are low, without any other indication of charge level. A low battery indicator compares the battery voltage against a voltage reference . Some cameras let you set the voltage reference based on the battery type, but most do not, so a compromise is made, at around 1.15volts where a NiMH battery will have 5-10% capacity remaining, and an alkaline will have about 40% of its capacity remaining. This is another reason why when the low-battery indicator comes on for NiMH batteries, the batteries are close to completely exhausted. The manufacturers tend to favor setting the level for NiMH batteries since these are most commonly used.

1. Simon Ramsdale, Strategic Marketing Manager, and Colin Davies, Applications Manager, Zetex Semiconductors

NOTE: The top voltage is for a fully charged battery, not under load. When under load, a fully charged battery will quickly fall to the rated voltage of 1.2 volts per cell.

There are two common ways of accurately measuring capacity on NiMH batteries. One is the pulse load test, and one is coulomb counting (how much energy goes in and out). Neither is implemented in any digital camera, due to cost and complexity. To do implement coulomb counting the battery must be charged inside the camera so the charging circuit can keep track of how much charge is put into the battery (or the batteries must be inside a pack that has the coulomb counting circuit), You can see an example of a "gas gauge" IC at http://focus.ti.com/lit/ds/symlink/bq2092.pdf. Such ICs are relatively inexpensive ($1 or so) but by the time you add the support circuitry, add in the extra printed circuit board space, and do the firmware, you've added several dollars to the manufacturing cost, none of which can be recovered by charging a higher price for the camera because so few users would understand why it was worth it to pay more for an accurate battery gauge.

"Ni-Cad [and NiMH] batteries provide a relatively flat voltage profile. The cell’s voltage will remain relatively constant for more than 2/3 of its discharge cycle. At some point near the end of the cycle, the voltage drops sharply to nearly zero volts. One disadvantage of using batteries with a flat voltage profile is that the batteries will need to be replaced almost immediately after a drop in voltage is noticed. If they are not immediately replaced, the batteries will quickly cease to provide any useful energy." U.S. Department of Justice New Technology Batteries Guide

"Maha NiMH battery remains at a high voltage even near the end of the cycle. Maha NiMH battery will hold full voltage (1.2v/cell) up to 80-90% of usage (varies on discharge rate)." http://www.nimhbattery.com/techfacts3.htm (Thomas Distributing).

Alkaline (manganese dioxide) batteries have a fairly linear voltage versus capacity curve which makes voltage based capacity measurements (under load) fairly accurate. The same scale is used in order to show the difference in linearity between alkaline and NiMH batteries. Alkaline batteries should be used only as a last resort in digital cameras because they are unable to deliver the high peak currents that most digital cameras require. I didn't realize just how bad alkaline batteries were until I lent an AA powered camera (Canon A570IS) to a relative that tried to use alkaline AA batteries while on a cruise. She reported getting about ten pictures per set of batteries. When I inquired if this was normal on rec.photo.digital I got a slew of responses and every one of them reported similar results with alkaline batteries.

Voltage Versus Capacity of a Four 2850mAH Alkaline AA Cells at 30 Degrees Centigrade (Discharge Rate Unknown)

Nominal Voltage of AA Batteries is Different for NiMH, Alkaline, and Lithium

AA powered cameras can use alkaline AA batteries (nominal voltage of 1.5V), as well as lithium AA batteries (nominal voltage of 1.7V) or NiMH batteries (nominal voltage of 1.20-1.25V). For some battery/vertical grip on some digital SLRs (which can often use Li-Ion packs, AA alkaline, AA NiMH, or AA Lithium) there is a software switch (in the camera) that you set to the type of battery you are using in order to have the battery gauge match the characteristics of the battery being used. There is just no way that a consumer level compact camera is going to implement such a software switch.

New alkaline batteries have a long shelf life, retaining about 90% of their capacity over five years. However there is one caveat to this long shelf life, it's for new, unused, batteries only. Alkaline batteries begin degrading as soon as you first use them, and the long shelf life is history. So if you're using alkaline batteries as emergency back-up, remember that once you start using them, you can't put them back in your camera bag for the next emergency. Use them up in other devices. http://web.mit.edu/2.72/www/lectures/Batteries.pdf page 3, states (referring to alkaline-manganese batteries): "The shelf life of the cell (in unused condition) is at least 3 years."

There are external battery testers for NiMH cells available that are able to indicate remaining charge using a pulsed-load method, but these are not inexpensive devices. You can order them from Thomas Distributing (click the images below). Some higher end battery chargers have one position that can be used to test remaining charge with a pulse-load test, for example, the Sanyo NC-MQH01U, but you still get only a general idea of remaining charge (0-50%, 50-80%, or >80). Of course to use these pulse load battery testers you have to remove the batteries from the camera which is a hassle.

NiMH and Ni-Cad batteries can exhibit a phenomena known as "polarity reversal;" Li-Ion batteries do not have this problem. Care must also be taken during discharge to ensure that one or more cells in a series-connected battery pack, like the common arrangement of four AA cells in series in a digital camera, do not become completely discharged and go into polarity reversal. Cells are never absolutely identical, and inevitably one will be completely discharged before the others. When this happens, the "good" cells will start to "drive" the discharged cell in reverse, which can cause permanent damage to that cell. To guard against polarity reversal, never completely discharge a set of batteries.

Note that on digital cameras, the camera will turn itself off before the voltage gets low enough to damage the cells. On devices that do not shut off automatically (i.e. flashlights and motorized devices) you want to be careful to not leave the device on accidentally and discharge the batteries completely.

With NiMH batteries each battery in a set of cells is slightly different. A frequent problem is a "dud" cell that affects the usage of the set. While it's easy to replace the dud cell, finding it requires an external battery tester, or an intelligent charger that can analyze cells.

— In most devices, usually two or more batteries are used together. When batteries are used in a series, the performance is limited by the worst one. In other words, one poorly performing battery can significantly reduce the device runtime.
— Battery matching refers to grouping batteries with similar “actual” capacity. To perform this, use the Refresh & Analyze mode to determine the battery capacity. Group batteries with capacity within about +/- 5% of the rated capacity.

Battery matching is a good idea if using NiMH batteries. Since capacity changes over time, batteries should be re-matched periodically. You need a charger like the Maha MH-C9000 or the La Crosse BC-900 to perform capacity matching.

AA powered cameras may come with two or four alkaline AA cells, but rarely does the manufacturer supply rechargeable batteries and a charger. This is a way to save expense on the part of the manufacturer. With a Li-Ion powered camera, the manufacturer always includes a charger and at least one battery in the box. Buying eight good NiMH batteries, and a good charger, can cost $40-$70 (depending on the features of the charger).

Li-Ion chargers are usually very small and do not require a wall wart--they plug directly into the wall and the battery slides in. Most NiMH chargers use a separate wall adapter. You can however find NiMH chargers with flip out plugs. They tend to be larger because the power supply is built in.

The reasons that the Li-Ion chargers are smaller are a) the charge circuitry is less complex because the battery pack has a lot of the circuitry inside and because detecting end-of-charge is simpler, and b) there is no need for individual slots with space between them so the temperature sensors for each cell can accurately measure each cell.

You can find smaller AA chargers, for example the Sony BCG-34HLD4 shown in the table above, but these are not full-featured chargers. For example, the Sony BCG-34HLD4 does not have four individual charging circuits, and it is very low-rate charger. The Sanyo NC-MQN05 is very small and light, but charges at a very low rate. Still, if overnight charging is acceptable, these small NiMH chargers are okay.

High Capacity Li-Ion Battery Packs are Comparable in cost to High Capacity NiMH batteries.

Say what? Yes, when you look at the big picture, including the maximum number of charge/discharge cycles, Li-Ion batteries actually can be less expensive than NiMH batteries, depending on which Li-Ion pack the camera uses. For example, let's compare using four 2500 mAH AA NiMH batteries against a single 1800 mAH BP511 Li-Ion battery pack. We'll also compare genuine Canon batteries, for both Li-Ion and AA, as well as the cheapest 2300 mAH AA batteries (which in all likelihood are not really 2300 mAH at all). I also added a row for the cheapest Li-Ion battery pack, sold on eBay under "Buy it Now." Also, many users will instead be limited by the approximate three year lifespan of Li-Ion batteries rather than by the maximum number of cycles. So I have included both typical and maximum number of cycles in the cost calculations.

The key in obtaining fresh, high quality, batteries at good prices, both for NiMH and Li-Ion, is to buy from an online retailer that specializes in batteries, and does a very high volume. For NiMH, the premier on-line retailers are Thomas-Distributing and AllBattery. For Li-Ion, the premier on-line retailer is SterlingTek. If you buy batteries from a big-box retailer or an on-line camera store, you will pay higher prices, especially for Li-Ion after-market packs (some on-line camera stores such as Ritz and Adorama do offer decent prices on after-market Li-Ion packs, but they are still more expensive than places that specialize in batteries).

Battery Type	Voltage	mAH	WH	Price	Price per WH	Typical Number of Cycles	Cost per Cycle (Typical)	Maximum Number of Cycles	Cost per Cycle (if Maximum number of Cycles is Achieved)
Genuine Canon BP511A	7.4 (3.7V *2)	1390	10.3	$48	$4.66	300 (3 years)	$0.160	1000	$0.048
High Quality Aftermarket BP511 (Adorama)	7.4 (3.7V *2)	1400	10.4	$20	$1.92	300 (3 years)	$0.067	1000	$0.020
High Quality Aftermarket BP511 (SterlingTek)	*7.4 (3.7V 2)**	2000	14.8	$12	$0.81	300 (3 years)	$0.04	1000	$0.012
Low Quality Aftermarket BP511 (eBay)	7.4 (3.7V *2)	1600	11.8	$3	$0.25	300 (3 years)	$0.010	1000	$0.003
Nikon EN-EL3e	*7.4 (3.7V 2)**	1900	14.1	$17.50	$1.24	300 (3 years)	$0.058	1000	$0.017
Canon NB4-200 AA NiMH (B&H)	4.8V (1.2V * 4)	2300	11.0	$20	$1.82	300	$.067	500	$0.040
High Quality Aftermarket NiMH AA	*4.8V (1.2V 4)**	2500	12.0	$10	$0.83	300	$0.033	500	$0.020
Low Quality Aftermarket NiMH AA	4.8V (1.2V * 4)	2300	11.0	$5.30	$0.48	300	$0.018	500	$0.011
Sanyo eneloop NiMH AA (four)	*4.8V (1.2V 4)**	2000	9.6	$10	$1.04	500	$0.020	1000	$0.010
Sanyo eneloop NiMH AA (six)	*7.2V (1.2V 6**	2000	14.4	$15	$1.04	500	$0.030	1000	$0.015

The high quality after-market Li-Ion battery is much less expensive, per cycle as the high quality aftermarket NiMH AA batteries, if the maximum number of cycles is achieved on each; Under more typical use, they are about equal.

Cost Difference of High Quality After-Market Li-Ion Battery Packs versus High Quality After-Market NiMH batteries
NiMH pricing is from Thomas-Distributing, Li-Ion pricing is from SterlingTek

The real picture is even worse for NiMH batteries in terms of cost for several reasons:

For very light users, NiMH batteries are cheaper by virtue of the fact that their lifespan is longer, typically five years for NiMH, versus three years for Li-Ion. However the absolute cost difference is still very small, we're talking $12 every three years versus $10 every five years. Oh my, that means that Li-Ion batteries cost twice as much per year, $4 versus $2! For light users It still makes sense to use Li-Ion batteries for all of the other reasons listed above.

Many people don't look at all the factors when comparing prices, and they end up comparing apples with oranges.

The cost of after-market Li-Ion packs depends on how popular the battery is. For example, the Canon BP511 and NB-1LH are the least expensive because they have been so widely used for so many years. I have two cameras that use the BP511, and one that uses the NB-1LH, so those are the packs that I'm most familiar with (I did not intentionally choose the cameras with the most widely available and least expensive battery packs, but it might be a consideration when choosing a camera). Less popular batteries are more expensive. I prepared a table of various battery packs, and their cost from various vendors. B&H is consistently the most expensive retailer for battery packs.

	Canon			Nikon			Minolta	Olympus
	BP511	NB-1LH	NB-2L	EN-EL3	EN-EL2	EN-EL1	NP-400	BLM1
Adorama	$20	$20	$19	$17.50	$27	$20	$30	$20
Amazon	$19	$20	$22	$17.50	$19	$15	$17	$17
B&H	$35	$30	$30	$34	$25	$24	$29	$30
Ritz Camera	$19	$14.50	$18	$17	$15.50	$25	$19	N/A
SterlingTek	$12	$9	$15	$18	$17	$12	$20	$17

How Good are After-Market Li-Ion Battery Packs?

The quality varies (just as the quality of NiMH batteries varies). You should stick to purchasing packs from a reliable retailer, and not buy the super-cheap ($3) battery packs on eBay. Sterlingtek has a very good reputation as a supplier of battery packs. However I was disappointed when I opened an old pack from Sterlingtek, and saw that while the pack was labeled as 1350mAH, the cells inside were actually only 1250mAH.

How Soon do the After-Market Battery Packs Appear on the Market, when a New Type of Battery Pack is Introduced?

Typically it takes several months for the after-market manufacturers to tool up to produce a new pack. For example, Nikon introduced a new type of battery pack for their D200 digital SLR, the EN-EL3e, and the aftermarket packs took a while to become available (Lenmar has one for $26, and no-name ones are available for less than $20). This battery pack has an internal micro-controller, so it took longer for the after-market packs to appear.

For products that are not very successful, there may never be after-market packs available. This is something to consider, because not only will after-market battery packs not be available, but the manufacturer may stop making the battery pack at some point. You can always send out your old battery pack to be rebuilt with new cells, but this is a hassle.

2CR5 Li-Ion Rechargeable Batteries

Many older digital cameras are able to use AA batteries or 2CR5 lithium batteries. There are now rechargeable li-ion 2CR5 batteries available. Ironically, the 2CR5 rechargeables are more expensive, and lower capacity than most after-market proprietary li-ion battery packs.

Li-Ion batteries are rather unique in that you can't just sell individual cells to end-users, you must have battery packs that have the proper protection circuitry, and you must have control of the charger circuitry. Even then there are often problems when a manufacturer screws up and you end up with a notebook computer in flames, or an exploding cell phone. However, unlike phones and computers, most camera batteries are charged outside the camera, so at least the camera will not be damaged by an exploding battery.

* This advantage is over Lithium-Ion batteries in general, and is not an advantage only of NiMH batteries.

Li-Ion Battery Packs are Proprietary*

Each manufacturer has its own battery pack design, and charges a lot of money for extra packs. For the less popular products, there is no incentive for third-party manufacturers to offer after-market batteries, so the user must pay high prices for spare batteries. However, after-market versions of the popular models of battery packs can be purchased very inexpensively (see http://www.sterlingtek.com/digital-camera-batteries.html). When choosing a camera, one consideration should be the cost and availability of after-market Li-Ion battery packs.

* This advantage is over Lithium-Ion batteries in general, and is not an advantage only of NiMH batteries.

For AA powered devices, if you are in the middle of nowhere and your batteries go dead, you can often get by with some AA alkaline cells. This point is valid, though the advantage is wildly overstated.

First of all, you are much less likely to have your batteries go dead in the first place if you are using Li-Ion batteries. Second, you can always charge your batteries from any 12-15V source, including a vehicle power outlet, solar panels or even a pack of ten or twelve AA batteries. Third, for popular digital SLRs, the optional battery grip can often use AA cells. Fourth, alkaline batteries work very poorly in digital cameras. The high current requirements of a digital camera are incompatible with the alkaline cell's high internal resistance; you'll be lucky to get 20 shots from a set of AA alkaline batteries in a typical digital camera. As one review on the The Digital Camera Resource Page stated, "The alkalines that come in the box will quickly find their way into the trash." I didn't realize just how bad alkaline batteries were for digital cameras until I lent an AA powered camera (Canon A570IS) to a relative that tried to use alkaline AA batteries while on a cruise. She reported getting about ten pictures per set of batteries. When I inquired if this was normal on rec.photo.digital I got a slew of responses and every one of them reported similar results with alkaline batteries.

Amusingly, you often see statements such as "gee, it's a good thing that my camera uses AA cells, because my rechargeable AA cells went flat, and I was able to buy some alkaline AA cells at a trailside trading post in the Himalayas." One person argued that if he were hiking in the Australian outback, 1000 miles from the nearest electric outlet, he could easily buy AA batteries at a convenience store (presumably a 7-11 operated by kangaroos, that had no electricity!).

The ITMON rationalization is especially amusing because if you were in the boonies, you'd want to bring along the densest, lightest, longest lasting type of batteries, so they wouldn't go flat in the first place, and if your li-ion battery went flat, the best use of the alkaline batteries would be to charge the Li-Ion battery!

There are NiMH chargers that can fully charge four cells in 15-30 minutes. Fully charging the same capacity Li-Ion battery pack will take several hours.

However there is a big "gotcha" in fast charging NiMH batteries, as fast charging reduces the service life of the cells, and often results in less complete charge.

"...when charging speed is not a priority, it would be more cost effective to select a slow charger, which also gives longer battery service life and enables fuller charge of a battery compared with a fast charger."

On the other hand, fast charging tends to use more of the available capacity of the battery. Buchman writes:

"NiMH batteries which use the NDV method or the thermal cut-off control tend to deliver higher capacities than those charged by less aggressive methods. The gain is approximately 6 percent on a good battery. This capacity increase is due to the brief overcharge to which the battery is exposed. The negative aspect is a shorter cycle life. Rather than expecting 350 to 400 service cycles, this pack may be exhausted with 300 cycles."

This is an advantage because this means that a single charger can be used to charge batteries from a variety of devices. It doesn't lessen the number of batteries that you need to carry. If your GPS, your camera, and your flashlight, all use AA or AAA cells, this means carrying only one charger, as long as you don't need to charge more than one device at a time. Unfortunately, you still need a separate charger for your cell phone, PDA, notebook computer, etc., since these devices use Li-Ion batteries for the most part.

In reality, you can use one charger for most of your NiMH and Li-Ion devices, the Lenmar Mach 1 Speed Charger, but you need to bring the appropriate adapter plates (very light, but somewhat bulky). It can be used in on 12VDC or on AC. Though I own one of these (an older version that also had a USB output charging port), I find that the Li-Ion chargers with integrated AC plugs, are more convenient.

* This advantage is over Lithium-Ion batteries in general, and is not an advantage only of NiMH batteries.

Li-Ion Batteries have a useful life of only about three years from the date of manufacture (though some battery experts claim up to five years). NiMH batteries have a shelf life of about five years, if kept charged. So with Li-Ion batteries, the battery will probably go bad before you even reach the maximum number of charge/discharge cycles, while the NiMH battery will probably go bad based not on the shelf life, but due to the number of charge/discharge cycles.

* This advantage is over Lithium-Ion batteries in general, and is not an advantage only of NiMH batteries.

For popular cameras, the availability of Li-Ion battery packs over the long term is not an issue. However for less popular models, it is possible that the camera could outlast the availability of battery packs. You can't stockpile Li-Ion battery packs, as they have a limited shelf life of around 2 years before they begin to lose their capacity. If you get stuck with no battery pack availability, your only option is to send an existing pack out for rebuilding with new cells. There are services that do this sort of thing. However at this point in time, there are no Li-Ion digital camera batteries that are not available.

There are battery chargers available for NiMH batteries that plug directly into the 5 volt USB port of a computer. Two cell and four cell models are available. While some smaller Li-Ion powered cameras, that use a single 3.7V Li-Ion pack, can be charged directly from a USB port, most cannot. Larger Li-Ion powered cameras use a two cell Li-Ion pack (7.4V) and there are no USB chargers available that boost the 5V output up for charging these higher voltage packs.

If you have an SLR or a high-end point and shoot that has an external hot shoe flash, the flash will take AA batteries. If the camera also takes AA batteries then you only need one type of batteries for both the flash and the camera.

This is only true in the rare cases when after-market Li-Ion packs are unavailable. You can purchase very high quality NiMH batteries (i.e. Panasonic or Sanyo) for about $2.25 each. So for a camera that uses four AA batteries, you can have a replacement set for around $9. But wait! You can purchase a replacement Li-Ion battery pack for most cameras for $9-15. A replacement battery for a Canon digital SLR like the 20D is $12 ($11.50 if you buy two at a time, less than $9 in bulk). A battery for a Nikon D70 or D100 is $10.

You can purchase lower quality NiMH batteries for very low prices, often around $1 each for 2000mA rated cells that have an actual capacity of around 1800mA. These lower quality cells are usually sufficient, especially with the faster chargers.

Be certain to take the number of charge/discharge cycles into account when comparing costs. Also take into account the fact that you'll need more sets of NiMH batteries due to the lower capacity, and higher self-discharge rates.

A Separate Charger is Required for Each Li-Ion Battery or Li-Ion Powered Device

It's even less of an issue, when you realize that you simply cannot buy an AA or AAA powered cell phone, PDA, camcorder, or notebook computer, so you're going to be stuck with multiple chargers even if you get a camera that uses AA cells. Furthermore, even if all your devices could be powered by AA or AAA cells, you still would be carrying multiple chargers so you could charge all of your AA cells at the same time.

Fortunately, chargers for most devices and Li-Ion batteries are quite small in size, much smaller than an AA battery charger, so it's not really a big deal to carry your chargers when traveling. The important thing to understand is that it's a total fabrication to claim that AA powered cameras are better because you can use the same charger for your phone, computer, etc., and not have to carry multiple chargers.

It is highly unlikely that the camera will outlast the availability of replacement battery packs. If you choose a very low volume camera with a battery pack that isn't used in many devices, then this might be a valid concern, but popular battery packs used by Canon, Nikon, and Sony, will be available for the life of the camera. Just look at the "proprietary" batteries that are no longer available for cameras. The only ones I know of are the mercury batteries, and some clever person came up with a Zinc-Air replacement. Worst case, you can have your existing pack rebuilt with new cells, but this is unlikely to be necessary.

I'm not making this one up, I swear! This is the sort of crap that you can find on rec.photo.digital, where a couple of individuals try to create stories to justify their position in the "battery wars." There are several errors of fact in that statement. First, buying batteries on eBay is generally a bad idea; you have no idea how good the products are, and you have no recourse if the seller doesn't ship you the product or if the product is defective, and the seller typically charges high shipping charges, but low prices for the product, to minimize their eBay fees, and to avoid having to refund much money if you return the product. Second, Li-Ion batteries that can be purchased at any one of a number of on-line camera stores, cellular phone accessory e-tailers, brick and mortar retailers, or battery specialty companies. Third, eliminating Li-Ion batteries from a camera doesn't help you much for cell phones, PDAs, notebook computers, camcorders, etc.

What is an issue is that buying the Li-Ion batteries at a brick and mortar retailer, versus ordering from Ritz, Adorama, B&H, Sterlingtek, Amazon, etc., is much more expensive (actually I don't know if Ritz's stores charge the same as their on-line store). You can buy NiMH AA rechargeables as cheaply (and often cheaper) in a store as you can on-line. Costco sometimes has high capacity AA NiMH cells that aren't bundled with a charger, for around $2 each.

When Traveling, All the Charger Cords Become Tangled Up with Other Items in Your Suitcase

Another gem from rec.photo.digital. Of course you really don't have much of choice to take your cell phone or notebook computer charger with you, when traveling. And most any NiMH charger that can operate off of both AC and a car cigarette lighter also has a cord. In fact, the very small Li-Ion wall plug chargers simplify your life. You can charge all your batteries simultaneously at night, rather than fumbling with a load of individual AA cells.

Most Li-Ion chargers do not have cords at all, they plug directly into the wall outlet and the battery fits into the charger. As to packing for a trip, wind the cords of cell phone and PDA chargers around the charger body, and insert the charger into a zip-lock bag. This protects the charger, as well as other items in your suitcase. In fact, I suggest buying various size zip-lock bags and using them extensively when packing. You can buy very large zip lock bags at Smart & Final, and other stores. I like to separate different types of clothing into individual bags, and of course toiletries are protected against leakage by double bagging.

For AA powered digital cameras that are not heavily used, i.e., a few hundred photos per year, it is better to use Energizer® AA Lithium Batteries. These AA cells have a very long shelf life, a negligible self-discharge rate, excellent low-temperature performance, a flat voltage curve, and are capable of providing the high current needed for fast recycling of the camera flash. A pack of four costs about $8.

Standard alkaline AA cells are not well suited for use in digital cameras. Alkaline batteries have a high internal resistance, and are not capable of delivering large amounts of current which is needed to rapidly recycle the flash. Alkaline batteries have poor low temperature performance. The voltage level of alkaline batteries declines linearly as it discharges. They can be used in a pinch, but are best avoided.

Ensure that there are chargers, either from the camera manufacturer, or after-market, that allow you to charge batteries in a vehicle, without the use of a DC to AC inverter. Lenmar makes a wide variety of such chargers.

Lenmar MSC1LX Mach 1 Speed Charger

This charger can charge nearly every Li-Ion camcorder or digital camera battery, as well as NiMH AA and AAA cells. This charger will end the excuses regarding Li-Ion batteries and multiple chargers! Buy from Thomas Distributing for $42. It's not an ideal NiMH charger, because it charges the cells only in pairs, but it's adequate for traveling when you don't want to carry multiple chargers.

The charger comes with adapter plates for the most common batteries, and you can buy plates for most other Li-Ion batteries (the Lenmar plate listing is incorrect, since many of the non-highlighted battery types actually are supported with the plates that come with the charger). It comes with one free adapter plate (download coupon) if you send them your UPC code and $3. Good camera stores that carry Lenmar will stock the plates ($10) each. This may be the only after-market Li-Ion charger available for the less popular Li-Ion digital camera batteries. Click for Complete List of Available Plates (this is from the Internet Archive and may be incomplete. Lenmar has removed the list from their web site).

Since the Lenmar site doesn't tell you what comes with this charger, I will. It comes with five plates, but each plate supports multiple batteries (this information is for an older model, I'm not sure if the plates that are supplied are still the same).

Plate for 4 AA/ 4AAA cells (must be charged in pairs)
Plate XPA1: Canon BP-911/914/924, Canon NB-2L, Samsung L110/L220/L160/L320/L480
Plate XPA3: Canon NB-1L/NB-3L, Olympus LI-10B, Nikon EN-EL1
Plate XPA4: Fuji NP-80/NP-100, JVC BN-V712U/BN-714U
Plate XPA5: Canon BP-511/BP-522, Nikon EN-EL3, Olympus BLM-1, Minolta NP-400

If you're planning to be away from grid or vehicle power for an extended period of time, these devices will allow you to charge your batteries from human or solar power.

For solar, you'll want the following items (all the links are to the items on Amazon):

1. Solar panel, about 15 watts (http://tinyurl.com/58tv2n)
2. Charge controller (http://tinyurl.com/5g3xfr)
3. 12 volt gelled electrolyte lead-acid battery (get a 7AH battery, as it's most common and inexpensive, unless size and weight are big concerns) (http://tinyurl.com/67mhzs)
4. DC battery charger for the Li-Ion packs (http://tinyurl.com/6jd4ox)
5. Cigarette lighter socket attached to the battery (get a 12 volt outlet splitter and cut off the plug and attach the wires to the battery) (http://tinyurl.com/6335kt)

The solar panel generates DC current that charges the lead-acid battery though the charge controller. The DC battery charger connects to the battery and charges the Li-Ion or NiMH cells. Most chargers require more current than the solar panel can provide on its own. The best regime is to let the solar panel charge the battery during the day, then use the battery to charge the camera batteries at night. It will take about eight hours of strong sunlight to charge a 12V 7AH lead-acid battery with a 15W solar panel, and this will charge about three 2000 mAH Li-Ion packs.

The 12V 7AH battery provides 78WH, while a typical D-SLR battery is about 14WH. Even allowing for the inefficiencies of the DC-DC charger, you can charge three Li-Ion batteries from just the energy inside a fully charged 78WH battery. Of course be sure that the lead-acid battery is fully charged before heading out. Bring along a butane powered soldering iron for any repairs that you may need to make to the set-up.

Buy a load of Energizer lithium AA batteries from Wal-Mart or Target, and at the end of the trip return what you didn't need (which is hopefully all of them). There are two ways to use the lithium batteries. If the camera accepts AA batteries, either directly or via a battery grip (D-SLR) then you're all set. You could also buy a 10AA battery holder with attach a cigarette lighter socket attached to it and plug the Li-Ion charger into the pack of AA batteries. Actually you're not limited to AA size in this case, you can use D cells. See http://www.minute-man.com/acatalog/Battery_Holders.html for battery holders. There are 10AA holders available, but for the D cells you'll have to combine a 4 cell and a 6 cell holder.

High-quality after-market Li-Ion battery packs are now so inexpensive that it may be more practical to just buy a bunch of them, charge them up, and forget about solar charging except for extremely long periods of time. I.e., I can buy twenty, 2000 mAH, BP511 battery packs for my Canon digital SLR for $168 ($8.40 each), This is cheaper than NiMH or Lithium AA batteries, and cheaper than the whole solar set-up. Twenty batteries would be good for at least 8,000 outdoor shots.

This device puts out 3, 6, 9, or 12 volts and has a 12 volt lighter socket. It takes a lot of cranking to charge the internal batteries, which in turn will charge whatever you plug into it. Buy it from Amazon for $47 plus shipping. I've received one. It's basically a 12V, 1.2 AH, sealed lead-acid battery that can be recharged by the dynamo, by an AC adapter that puts out 12VDC, or by a car cord. The lower DC voltages are obtained from a linear regulator, and are limited to 200 mA. Charging by cranking is really for an emergency, as it would probably require several hours of cranking to fully charge the internal battery. The radio and flashlight are cute, but of low quality. The battery level indicator, which consists of three LEDs, is worthless, since the internal battery has a fairly flat discharge curve, and it shows that the battery is at full capacity, even when it's almost totally discharged (flashlight bulb barely illuminated). This probably isn't something that you'd want to carry backpacking.

Search at http://www.cabelas.com for "Brunton Solar," Cabela's appears to have the best prices.

Brunton makes a variety of solar powered chargers. The SolarPort 4.4 is cascade-able to increase the output. You can purchase solar panels for a lot less, but the Brunton products are conveniently packaged for portable use.

There is an excellent web site about NiMH battery chargers available at http://nordicgroup.us/chargers/. The site is limited to NiMH chargers that meet the following criteria:

Tenergy T6278 Universal (AAA, AA, C, D, 9V) Smart Charger Review

While there are numerous smart chargers available for AA and AAA cells, there is a dearth of smart chargers for C & D cells. C & D cells are finally coming down in price, and low-discharge C & D cells are also now available. I was looking for a good C & D charger because I use a lot of C batteries in Cree LED flashlights (the awesome Taskforce 2C Cree LED flashlight from Lowe's) for bicycle lighting. I finally saw what I was looking for in the Tenergy T6278 (specifications).

There are individual charging channels with the LCD display for each channel. There's a fan to keep the batteries cool during charging, which also helps to prevent false over-temperature detection which would prematurely shut the charger down. The charge current is 1000 mA for AA, C, & D, 500 mA for AAA, and 13 mA for 9V, with trickle charge current of 100 mA for AA, C, & D, 50 mA for AAA. While the batteries are charging, the LCD display shows the bars moving up. When the batteries are discharging, it shows them moving down, then when the battery is fully-discharged it begins charging it (some channels can still be discharging while others are charging). At conclusion of charging, the LED for each channel changes from red to green, and the charger switches to trickle charge at 100mA (trickle charging above 0.05C (1/20th of the battery capacity is not recommended, so don't use NiMH batteries under 2000 mAH). The LCD will also indicate if the battery is bad.

There is a discharge feature since periodic deep discharge is crucial in maintaining NiMH batteries (all batteries must be discharged at once, you can't discharge individual cells because there is only one button to start the discharge process. It takes a long time to discharge the 5000 mAH C cells, at least 20 hours. I checked the discharge current and it was 200 mA (I was timing it but was interrupted by a power failure).

The power adapter is rated at 12 volts, 1.2A, so the charger could easily be used from a vehicle's 12 volt power source without the need for an inverter, but there is no DC charging cord offered so I'm going to fabricate one. The resellers of this charger should really offer a 12 volt cord with a cigarette lighter plug.

One potential problem is that the charger stops automatically after six hours of charging (most good chargers will time-out just in case the Delta V charge detection or the over temperature detection doesn't stop charging). A fully discharged 10,000 mAH D cell will take about 14 hours to charge (extrapolating from the charging timetable (2.8 hours for a 2000 mAH cell)). Even the 5000 mAH C cells that I bought would take about 7 hours to charge from a totally discharged level. The next design should either extend the maximum time, or include a switch to select 6, 12, 18, or 14 hour cut-off.

The instruction manual is printed on three sides of the box (in English and German) which is kind of a pain to not have them on a sheet of paper.

It also charges 9V NiMH batteries (usually 8.4V in practice), but it doesn't do the discharge function for them.

I'm not sure if the end of charge detection is ∆V or -∆V. Normally there would be a switch for Ni-Cad (-∆V) versus NiMH (∆V) to switch the end-of-charge voltage detection. The box just mentions "∆V control."

All in all, it's the best C/D charger I've found, and I've looked at a lot of chargers. Of course it also charges AA and AAA cells, as well as 9V batteries.

I ordered this charger from one of AllBattery's eBay "Buy it Now" auctions (where the prices can be less than their web site, though with higher shipping). Since they are close by to me, and I go over to that area often, I called to see if I could do Will-Call and they said it was fine, though they still charged $4 "handling" for me to pick it up. I got the bundle with 8 5000 mAH C cells for $60, including handling, plus tax.

http://www.all-battery.com/index.asp?PageAction=PRODSEARCH&txtSearch=June002&SetPageSize=25

Note that if you navigate away from their web site without ordering you'll often get an offer for a 10% discount via chatting with someone (or something). This still was more than the eBay price for what I ordered so I declined.

Two promotional codes to try at AllBattery are tenergy2008 (free shipping) and battery12 (12% off).

A computer's USB port supplies a minimum of 500mA of current at 5 volts. This is sufficient for overnight charging of NiMH batteries (with four batteries, the charging current will be about 250mA per battery at about 1.8 volts). See http://nordicgroup.us/chargers/ for a list of these chargers. The most versatile unit allows charging from AC (flip out AC plug, no wall wart), a DC car cord, or a USB port.

While it is not possible to have rechargeable Li-Ion AAA, AA, C, or D cells, there are some somewhat standard Li-Ion batteries available. CRV-3 batteries are available in a rechargeable package, RCRV-3, from several manufacturers (the charger and batteries are not interchangeable among manufacturers). CR2 Li-Ion cells are also available. Ironically, the "standard" cells are both more expensive, and less convenient than proprietary Li-Ion battery packs.

If you have an AA powered camera, check to see if it can use RCR-V3 batteries instead of AA cells. These are rechargeable Li-Ion battery packs that are the size of two AA cells. Many AA powered cameras can use them, but it depends on the battery compartment dimensions. See http://www.delkin.com/pdf/product_docs/rcr_v3.pdf for more details. The down side of these batteries is that they are about four times as expensive as a Li-Ion battery pack (you need two of them for a camera powered by four AA batteries), and you'll need two chargers to charge a set of them at once.

Li-Ion batteries are considered low maintenance batteries. They have very low self-discharge. They have a high number of charge/discharge cycles. They do not benefit from complete discharging, prior to recharging like NiMH batteries. There is no "memory effect." The chargers are simpler, because detecting end-of-charge is very easy, and because protection circuitry is integral to the battery pack.

And finally....don't worry too much about all of this, because high-capacity, high-quality Li-Ion battery packs are available after-market for about the same cost as NiMH AA cells, when you factor in watt-hours and number of cycles.

Vast quantities of low quality NiMH batteries are flooding the market. Be very careful to not go just by price and rated capacity when selecting NiMH batteries, because often the rated capacity bears absolutely no relation to the actual capacity. You can see tests of various NiMH cells at http://www.candlepowerforums.com/vb/showthread.php?t=79302. There are 2300 mAH cells with actual capacity of about 1300 mAH, and their are 2300 mAH cells with actual capacity of 2200 mAH. There are 2500 mAH cells that are actually only slightly higher capacity than competing 2300 mAH cells. If the actual capacity is more than 10% less than the rated capacity, then it's a good idea to avoid that brand of batteries completely.

Personally, I'd stick with Energizer, Sanyo, and Panasonic, and buy one step below the highest capacity. You can buy a four-pack of Energizer 2500 mAH AA cells for around $8.25, versus a four-pack of Accupower 2600 mAH cells for about $12.75. There is an actual capacity difference of about 100 mAH, but the Accupower cells are more than 50% more expensive. The highest capacity cells are always priced higher per mAH than the next step down.

Costco now sells a Sanyo eneloop "Power Pack" consisting of eight AA cells (2000mAH), four AAA cells (800mAH), two C size adapters, two D size adapters, and an NC-MQN05 charger for $26.49. This is a very small, and very slow charger. The total value of the package is about $47, assuming you'd purchase all the components. Note that with the C adapters the length of an AA cell is greater than the length of a C cell, so not all devices can take the adapters. This is a high-demand item, and may go out of stock.

You can use the Sanyo eneloops in nearly all your battery powered equipment. As explained earlier, It's best to avoid completely discharging NiMH batteries by leaving a device on indefinitely. Cameras turn themselves off either based on time or voltage, but a set of series connected NiMH batteries in a flashlight could have cells damaged by polarity reversal. Note that some NiMH battery manufacturers claim to have protection against polarity reversal built into the cell, but in fact this is untrue.

Be careful about the Sanyo eneloop look-alikes that are starting to appear at stores like Wal-Mart. The new Kodak "Pre-Charged" batteries and the Rayovac Hybrid batteries are not as low-discharge as the eneloop batteries.

As Isidor Buchmann writes (http://www.buchmann.ca/), NiMH cells are considered high maintenance batteries. This is due to the self-discharge, the low number of charge/discharge cycles, the so-called "memory effect" (which is very real), the lack of trickle charging on most chargers, and the priming requirement. NiCad batteries are actually lower maintenance, and continue to be used in more critical applications, despite their lower energy density.

And finally....don't worry too much about all of this, because high-capacity, high-quality NiMH batteries (at least AA cells), cost only about $2 to $2.50 each. If you mistreat them, you may only get 150 cycles rather than 300 cycles out of them, which is no big deal!

Trading Cycle Life for Capacity

Battery experts all agree that doing periodic refresh cycles (full discharge/full charge) helps to maintain the full capacity of NiMH batteries. The refresh cycles reduce crystal formation in the battery, preventing the electrolyte from contacting the active material.

With Ni-Cad batteries, which have a much higher cycle life than NiMH batteries, the recommendation was to do a refresh charge every month. NiMH batteries have a far lower cycle life, typically 300-500 cycles, but often lower. The recommendation by Maha (in the MH-C9000 battery charger manual) is to do a refresh every ten non-full-discharge/full charge cycles, and to perform the break-in mode regimen every 30 cycles. Buchmann recommends once every three months.

In my opinion, the cost of NiMH batteries is now low enough that slightly shorter cycle life is a worthwhile trade-off in order to maintain the maximum battery capacity.

Warning! Apparently there are counterfeit Sanyo batteries flooding the market. Sanyo batteries are identified by "HR" stamped into the metal of the negative terminal. Other NiMH battery manufacturers are apparently stamping their negative terminals with the same "HR." Thomas-Distributing now emphasizes "with Printed Sanyo Label" on their web site description of Sanyo industrial batteries. Some Sanyo industrial batteries have an unprinted dark green plastic sleeve. If a retailer claims that their no-name batteries are actually Sanyo batteries, be very wary.

This charger includes a cable to charge from a car power outlet, charges each cell individually, does not charge at a very high current, and has a lifetime warranty.

To keep large numbers of batteries topped off, without damaging them, you can build a charger that continuously supplies a very low charge current (10mA.or so to the pack) I do this because it enables me to keep fresh batteries, ready to use, available for my kid's toys, FRS radios, etc. It also prevents the batteries from going bad, which will happen if you let them sit around for long periods of time uncharged. You could not really charge a fully discharged battery with this charger (it would take hundreds of hours), but it's fine for keeping quantities of batteries ready to use, without damaging them. Note that NiMH batteries should not be trickle charged at rates higher than about C/100 (capacity/100). So a 2300mAH battery should be trickle charged at no higher than about 23mA. In reality 10mA is sufficient.

The cost of such a charger is very low, it's just some diodes, resistors, battery holders, and a regulated AC adapter that can put out around 7.5V.

Theory
For four batteries, you need to supply a minimum of 6.6V (1.65 x 4) to each pack. Since the packs need to be isolated from each other (you cannot charge NiMH batteries in parallel), a diode is used on each pack, which also drops the voltage down by 0.7V. So you should use a 7.5V, regulated, AC adapter. The voltage to the packs doesn't have to be precise, but it should be somewhere between 6.5 and 7.5V, after accounting for the diode drop.

Empirical Measurements
Using this charger, I measured the current flow through a set of four fully charged Sanyo 1800mAH AA cells (1.43V per cell, no load), and it was about 10mA. Measuring the voltage of the four-pack, when not hooked to the charger it was 5.72V, when hooked to the charger it was 5.73V. The no-load voltage at the battery holder terminals, when open circuited was 7.4V.

Note that even 10mA of trickle charge may still be bad. As Isidor Buchmann writes, "It is best to store batteries on a shelf and apply a topping-charge before use rather than leaving the pack in the charger for days. Even at a seemingly correct trickle charge, nickel-based batteries produce a crystalline formation (also referred to as ‘memory’) when left in the charger. Because of relatively high self-discharge, a topping charge is needed before use."

There is freeware firmware called CHDK available for many Canon point and shoot cameras, adding many firmware features found only in D-SLR cameras. This firmware adds features such as:

CHDK provides a battery gauge in cameras that normally don't have a percentage indicator. Unfortunately, the default settings for the top voltage (Battery MAX Voltage (mV)) and the bottom voltage (Battery MIN Voltage (mV)) are often not correct. Some versions of CHDK will display the actual battery voltage as an option but many do not.

For example, on my SD series Canon P&S, the default for Battery MAX Voltage (mV) was set to 4.1V. Probably they based this on the fact that a fully charged, single cell, Li-Ion battery will read about 4.1 volts when it's not under load. However as soon as it's placed in the camera, and the camera is turned on, the voltage immediately falls by at least 100mV. So CHDK will not show 100% capacity even though the battery is fully charged, and some users might be concerned that there is something wrong with their battery or charger. Fortunately, it's an easy fix, since CHDK allows you to precisely set the battery voltage for both Min and Max. It may take several tries to get the right voltage for the MAX value. You should set the MAX voltage to where the battery indicator just goes from 100% to 99% with a fully charged battery. The battery parameters are accessed at Advanced Menu > OSD Parameters > Battery Parameters.

While I've found CHDK useful, remember that it doesn't turn a P&S camera into a D-SLR. The P&S will still suffer from more noise, less dynamic range, and slower auto-focus/shutter lag.

An oft-asked question is why "they" don't make 1.5V AA Lithium-Ion rechargeable batteries? Wouldn't such batteries enable users to gain all the benefits of Li-Ion batteries while retaining the ability to buy standard AA batteries in an emergency? There are several reasons why there's no such animal as a 1.5V rechargeable, Li-Ion, AA cell. First, the chemistry of Li-Ion yields a cell voltage of about 3.7 volts, while AA batteries range from 1.2V (NiMH) to 1.7V (lithium). Second, Li-Ion battery packs for cameras, which consist of one or more 3.7V Li-Ion cells, have protection circuitry built into the pack to protect against over-charging which can result in fire or explosion; each AA size li-ion cell would require the protection circuitry to be built into the cell, and it would be uneconomical to duplicate this circuitry in every battery. Third, such batteries could not be charged with a standard NiMH AA charger (unless even more circuitry was built into each cell).

There have been attempts to use the 2CR5 Li-Ion pack as a replacement for two AA cells, to enable AA powered cameras to benefit from Li-Ion technology. A few D-SLR and point and shoot cameras can use this battery, but the "standard" 2CR5 costs more than proprietary Li-Ion packs, so there's little advantage in this approach.

While technically it would be possible to build circuitry into an AA size cell that would convert the 3.7V down to 1.5 volts or so, and to enable charging in a regular AA charger, this would be a complicated and expensive solution to a problem that doesn't really exist.

AA sized Li-Ion cells do exist, but please don't call them AA cells! The designation is 14500, and they are relatively inexpensive. They have protection circuitry built in. They need to recharged in a Li-Ion charger, and the voltage is 3.7V, so they are not interchangeable with "standard" 1.2V to 1.7V AA batteries, except in some devices that have internal switching regulators. For example, many high end LED flashlights have internal switching regulators that can accept a wide range of voltages (they can run off one or two standard AA batteries, or a 3V CR123 battery, or one 14500 battery). In terms of capacity, there is a slight advantage with these cells, versus low-discharge NiMH cells; a 3.7V, 900mAH cell yields a capacity of 3.33WH, while an AA Sanyo Eneloop yields a capacity of 2.5WH.

3.7V is a little too high even if you used a dummy cell in series with one of these batteries in a device that uses two standard AA batteries (the voltage per cell would average out to 1.85V).

It would be nice if manufacturers of AA powered cameras were to design them to operate at a range of voltages from 2.4V (two NiMH AA cells) to 7.4V (two Li-Ion 14500 cells). This wouldn't be very hard to do, after all it's already being done in relatively inexpensive flashlights. All that is needed is a simple buck/boost switching regulator. They also would need to be able to program the battery type into the camera so the battery level gauge or indicator would work properly (some cameras already have this feature). For example, look at the UltraFire Cree C3 Flashlight with 2xAA Extension Tube Bundle. It works with an input voltage of 0.8V to 4.2V. See the table below for the different battery combinations. They do warn against using two 14500 lithium-ion batteries since the circuit cannot accept 7.2V (it's more difficult and expensive to design a switcher with such a wide input voltage range).

Two-Pack of Li-ion 14500 Cylindrical Rechargeable Cell: 3.7V 900mAh from DealExtreme

There are a variety of solar panels that put out 12VDC, then you plug a standard 12VDC capable Li-Ion charger into them. Not the most efficient system, but no one seems to want to build custom chargers. See http://www.solarhome.org/search.aspx?find=digital+camera for details.

By the way, there are no waterproof AA powered digital cameras available, I've looked. I wanted something for my daughter's week long canoeing trip from Minnesota to Canada. The best solution was just to buy some spare Li-Ion packs.

The Kodak Easyshare Z612 and Z712 IS can use a variety of battery types. It comes with a CR-V3 disposable Li-Ion battery, it can use the Kodak KLIC-8000 rechargeable Li-Ion pack, and it can use Energizer AA disposable lithium cells. The only AA cells that should be used are the Energizer lithium AA cells. Kodak does not specify NiMH or alkaline AA cells. While NiMH AA cells and alkaline AA cells will physically fit into the camera, they are not recommended because the voltage of the lithium cells is significantly higher than that of NiMH cells. Alkaline cells are high enough voltage, but cannot supply sufficient current due to higher internal resistance. The KLIC-8000 is the best choice for the Kodak Easyshare Z612 and Z712 IS. There are after-market generic replacements that are fairly inexpensive.

NiMH batteries will work for a short time in the Z712, but you'll go through multiple sets of NiMH cells for the same number of photos of the KLIC-8000, CR-V3, or Lithium AA cells. The NiMH batteries won't even really be discharged, but the voltage will be slightly lower than the fully-charged voltage, and this will result in the camera shutting down. There are numerous reports of attempts to use NiMH AA cells in the Z712, and they don't work well. Kodak could have made the cut-off voltage programmable so that NiMH batteries would work properly, but they didn't.

It's important to look at the big picture when comparing battery types, rather than just looking at the cost per cell or cost per pack.

Li-Ion rechargeable batteries have the following advantages over NiMH rechargeable batteries:

NiMH rechargeable batteries have the following advantages over Li-Ion rechargeable batteries:

Rebuilding Battery Packs when Recent Date Code Replacement Packs are Unavailable

This applies less to cameras, and more devices that use battery packs composed of standard cylindrical Li-Ion cells. This includes many laptop PC packs and portable DVD players as well as cameras that don't use the flat pack (prismatic) Li-Ion batteries.

First, before going down this road, check various sources for after-market replacement packs. Often you can buy current date code replacement packs that are not available as OEM packs (original equipment manufacturer). Some places to try are http://www.level8technology.com/, http://dealextreme.com/, and http://sterlingtek.com/. You'll often find that the difference in cost between replacing six 18650 cells and buying a whole new pack is not worth the minimal savings of hacking it yourself.

To rebuild a pack, first you have to open it. Some larger packs have tiny screws and snap latches, while some are glued shut. The glued packs can usually be opened by running an Xacto knife along the seam.

Once the pack is open, you need to figure out what size cells are inside. This will normally be printed on the cell, but you can also measure the dimensions of each cell and match things up that way.

Common Li-Ion Cylindrical Cells

Type	Length	Diameter	Volts	Typical mAH
14500	49mm	14mm	3.7	900
18500	50mm	18mm	3.7	1300
18650	65mm	18mm	3.7	2200
26650	65.5mm	26.5mm	3.7	3100

Order replacement cells from a place like http://www.all-battery.com/li-ioncylindricalrechargeablebatteries.aspx (watch the video). Be sure to order cells with solder tabs spot welded to the terminals, but you don't need "PCB Protected Cells."

Take some photographs of the inside of battery pack assembly before you replace the cells, and draw a diagram of how the cells hook together and to the controller board, and how wires are routed, and how any insulating tape or foam is placed. The cells may not all be connected in series, or if they are in series there may also be wires connected between series connected cells. These wires allow cells to be charged in parallel (for faster charging) even while being discharged in series. Also be sure to look for the small thermal sensor and place it in the same place (usually stuck to one of the cells) from which it was removed.

Copy the existing connections exactly, including replacing any heat shrink tubing that is used on the tabs or on the wires connecting to the tabs. Soldering two tabs together is easy, soldering a wire to one tab is easy but soldering two tabs and a wire together can be tricky. I tin all the connections with solder first, then use wooden chopsticks to hold the wire and the two tabs together while I apply heat to the connection (this avoids cold solder joints). If you think you need any extra insulation between closely packed cells you can insert a piece of unshrunk heat shrink tubing.

I've only had to rebuild packs on stuff like DVD players. For common notebooks, cameras, and cell phones, replacement batteries are usually available for years or decades after the time of production.

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If you are disputing information in this site, please include references and citations to support your statements. I'm happy to fix mistakes if something is actually incorrect, and have made several corrections since the launch of this site.

Steven Scharf is an electrical engineer living in Silicon Valley, specializing in portable power design for embedded systems.

Model	Canon BP-511	Sanyo NC-MQH01U	Maha MH-C9000	Sony BCG-34HLD4	Sanyo NC-MQN05
Battery Types	BP-511, BP-512, BP-522, BP-532	AA/AAA	AA/AAA	AA/AAA	AA/AAA
Weight (g)	123	151	475	100	120
Volume (cc)	175	317	1060	191	213


Solar Panel	Charge controller	Battery	Li-Ion/NiMH Charger	Lighter Socket


Battery Gauge on Nikon D200 top LCD Panel. Gauge displays a good indication of remaining capacity when camera is powered by Li-Ion Rechargeable Battery Pack.	Low battery indicator on Canon S3 IS, a higher end AA powered camera. No battery gauge, just a "low battery" indicator because this is all that's possible for cameras using standard, user-replaceable, NiMH batteries.

Quantity	Size	Chemistry	Voltage
1	AA	Alkaline	1.5
1	AA	NiMH	1.2
1	AA	Lithium	1.7
1	14500	Lithium Ion	3.6
2	AA	Alkaline	3
2	AA	NiMH	2.4
2	AA	Lithium	3.4


ZTS Mini Battery Tester	ZTS MBT-1