AA & AAA Rechargeable Battery Basics


Post by WildSnow.com blogger | December 1, 2014      

Double A (AA) batteries are ubiquitous. Smaller AAA batteries run a close second on proclivity. Chances are you use these miracles of modern chemistry in your avalanche transceiver, headlamp, 2-way radio, GPS, camera…

Tester is essential gear no  matter what kind of batteries you run.

Tester is essential gear no matter what kind of batteries you run.

While all manner of amazing battery technology is on the horizon, the best options available in AA and AAA consumer cells are the rechargeable nickel-metal-hydride (NiMH for short), and the Energizer single use Lithium. (Also, rechargeable lithium-ion “power packs” are also a viable player, provided you have a compatible device). This blog post covers the basic NiMH AA and AAA rechargeable side of the equation.

NiMH batteries can be acquired in fairly high capacity versions, and can be recharged at any time in their duty cycle. Nmh performs well when cold, and one rechargeable NiMH battery will save you from buying and discarding dozens if not hundreds of single use batteries. These batteries are recyclable, and provide guilt-free trashing as they contain mild toxins in contrast to nicads, which contain cadmium. Set yourself up with NiMH — you’ll save money, and you’ll save the planet.

Capacity of batteries is commonly given in milli-amp-hours (mAh for short). The higher the milli-amp number, the longer the cell will last in use. A good quality alkaline battery yields about 2,600 mAh at room temperature, while a decent capacity NiMH with limited self discharge is generally around 2,000 mAh, with better NiMH equalling or surpassing Alkalines at ratings around 2,700 mAh (or much more, without the limited self discharge feature). More, NiMH does better when the temperature drops — causing them to easily exceed alkaline in performance. So in real-world use you can be way ahead of the game if you’re set up with nickle metal hydride. (Example, if you can get a good deal on Panasonic Eneloop batteries, they’re an ok buy but be sure you get the 2000 mAh version, they also make a cheapo 800 mAh version.) Panasonic BK-3MCCA8BA eneloop AA New 2100 Cycle Ni-MH Pre-Charged Rechargeable Batteries, 8 Pack

When you get serious, what NiMH batteries to buy? Budget versions can be useful if you’re doing “industrial” work such as a commercial photographer with multiple on-camera flashes requiring dozens of batteries. Problem is, cheapo NiMH batteries can be significantly lower in capacity, lack quality, and they rapidly lose their charge during storage. Thus for the casual user who wants to charge-and-forget the spare batteries kicking around in their glovebox and backcountry repair kit, higher capacity NiMH batteries that hold their charge in storage are probably a better long-term value.

To get the most bang for your buck, buy and use your NiMH batteries in sets. When you receive your batteries mark with the date and a number or color code. If the battery has a plastic coating that doesn’t accept marking, lightly sand a patch with fine-grit sandpaper and mark with a Sharpie. When grouping batteries in a device always use singles from the same vintage set.

If you’re detail oriented, attempt to roughly equal the number of charge cycles for every battery in a set, though going to this extent of battery management is a bit much for most of us. (In olden days it was also important to charge groups from the same set, but modern chargers handle each battery individually so this extent of battery worship is no longer necessary.)

Occasionally test your rechargeable batteries. Do so by pulling the cells out of your powered device when they’ve been run down and nearly discharged, but are still showing some juice (such as a dim headlamp). Check each cell with a battery tester such as the Radio Shack 22-093. If any cell measures significantly lower than the others, discard it. It’s best to use a battery tester rather than a volt meter, because a battery tester places a small load on the battery and gives you a more realistic read (some volt meters have a battery test function that does the same thing).

You can ruin your NiMH batteries if discharged to rock bottom. Here’s why: No two batteries are exactly the same. In a deep discharge situation the fresher battery may reverse charge and damage its exhausted neighbor. Fortunately many (if not most) sophisticated electronic gadgets have a low-voltage shutdown that protects your batteries from deep discharge. Again, as mentioned above, using your batteries in dated sets will help prevent damage from unequal pairing.


What’s the best way to charge your precious little NiMH cells? First, consider the speed of charging. You’ll see chargers claiming “fast,” “one-hour,” “rapid,” “trickle,” “overnight,” and more. All rechargeable batteries wear out, and the slower speed chargers can give you a few more charges over the life of the battery. Nonetheless, the convenience of fast charging could be worth the slightly reduced battery life. A good bet for a charger is the Knox 16 Bay, Amazon link to right. The Knox has an automobile adapter and even comes with a set of batteries to get you started.

Battery size dilemma: Chances are you carry backcountry devices that need both AA and AAA size batteries. If you’re attempting to downsize your repair kit, carrying both sizes is a buzz kill. Solution is the battery up-sizer (convertor). These handy devices consist of a plastic tube that re-sizes the battery up to the next largest size. As AAA and AA cells have the same voltage, doing so is not usually a problem. In my lightweight kit I carry a set of spare AAA cells in the adapters, ready for use in all manner of devices. Size converters are not perfect. By fault of the electrical characteristics of the AAA battery, or the slightly different size of the adapter (the AA size adapter is slightly thicker than the norm), you may not be able to adapt your AAA cells to all your AA devices. Buy a set and test, chances are you’ll be able to eliminate those AA batteries from your repair kit by simply carrying AAA cells in the adapters.



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Comments

5 Responses to “AA & AAA Rechargeable Battery Basics”

  1. Kit January 28th, 2015 3:21 am

    Hi! Lots of folks recommend never using rechargeable batteries in a transceiver; what are your thoughts on this?

  2. James Phiney February 19th, 2015 12:41 am

    Great blog! Hopefully many people will find best stuff about AA and AAA batteries from this article.

  3. CT March 17th, 2015 3:04 pm

    I am considering the Knox charger your recommending but wanted to know how decent the batteries are that come with the charger. Does anyone have experience with them?

  4. Big Steve December 29th, 2015 8:52 am

    Kit, avy beacons designed for 1.5V (nominal) alkaline cells work fine with 1.2V (nominal) NiMH cells, but beacon manufactures advise against using NiMH cells because most avy beacon battery life indicators are designed to work with alkaline cells. Alky and NiMH cells have different voltage discharge curves. A fresh alky cell has a higher initial voltage and the voltage starts to diminish gradually, i.e., a gradual voltage discharge curve. OTOH, a fully charged NiMH cell has a lower initial voltage, and a flatter discharge curve that falls off abruptly at the end of its charge cycle. The respective discharge curve lines cross pretty early in the discharge cycle, so, although a NiMH has a lower initial voltage, it has the same or greater voltage for much (often most) of its life vs. an alky cell. So, a NiMH cell in an avy beacon with a battery life indicator (designed for use with alky cells) will indicate, say, 60% cell life, when in fact, the cells may be only 10% discharged, i.e., have 90% life left on their charge cycle. The problem happens on the other end of the discharge curve (if you are relying on the beacon’s battery liffe NiMH cell might show 50% battery life but, in fact, have only 10% of life left. So, the take away is that NiMH work fine to power avy beacons but only so long as you do not rely on a battery life indicator designed for alky cells.

  5. Big Steve December 29th, 2015 9:04 am

    Oops, that was a bit wordy. Let me try to condense that:

    Most avy beacon battery life indicator circuits are designed to work with alkies, which have a different voltage drop curve (1.5V fresh then gradual decrease to 1.0V) than NiMH (c. 1.3V fully charged then flatter voltage curve @ 1.2V, then sudden dive). NiMH cells power avy beacons just fine, but the battery life indicator readings are of no use, e.g., you can go from an ostensible “70%” life to not working in a very short time. That’s why beacon manufacturers advise against NiMH cells.

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