AA & AAA Battery Mysteries Revealed!

By Louis Dawson

Battery adapter shown above converts AAA battery to larger size AA. Essential if you travel away from civilization and carry devices that use both sizes!

Double A (AA) batteries are ubiquitous. Chances are you use them in your avalanche transceiver, CD player, headlamp, 2-way radio, GPS, camera... Indeed, for the sake of simplicity it's a good idea to only purchase and use portable electronics that run on double A's. That said, many downsized electronic devices now run with tiny AAA cells. Until recently, I avoided carrying anything but AA size batteries and compatible devices, but that's changed because the smaller LED headlamps all use AAA cells, as do some of the downsized 2-way radios, and my favorite avalanche beacon. What's a backcountry person to do?

The solution to battery size problems for backcountry skiing and other outdoor recreation 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. I now carry a set of spare AAA cells in the adapters, ready for use in all manner of devices. You can order battery upsizers online from CYBERGUYS!®: Accessories Order a few extra, since they're dirt cheap and of average quality. Also, by fault of the electrical characteristics of the AAA battery, or the slightly different size of the adapter, you may not be able to adapt your AAA cells to all your AA devices. During my testing the AAA batteries in an AA adapter worked for me most of the time, but would not power my digital camera. Note that the adapters come in a set of different sizes. They work well for AAA to AA conversion, but the larger size converter (AA to C) that comes with the kit is slightly long, and may not work in all devices.

Batteries are expensive and cause pollution if disposed of in landfills. You can get rechargeable alkaline batteries, but they don't hold up well and have poor cold weather performance. Nickel Cadmium cells are better, but still lack capacity and pollute unless disposed of properly . While all kinds of amazing battery technology is on the horizon, the best generally available is the nickel-metal-hydride, or Nmh for short. These batteries have high capacity, may be recharged at any time in their duty cycle without the dread "memory effect," and they perform well in the cold. What's more, one rechargeable Nmh battery will save you from buying and discarding hundreds of alkaline batteries -- and Nmh batteries are the least harmful to our environment when discarded.

Capacity of batteries is given in milli-amp-hours (mAh for short). The higher the milli-amp number, the longer the cell will last in use. Nickel metal hydride AA cells are commonly available in 1100 to 1800 mAh, with the best compromise between cost and performance being the upper range. Indeed, if you look at the cost of buying regular alkaline or lithium batteries, buying the 1600 mAh rechargeable Nmh is a terrific value -- they pay for themselves after just a few use cycles. A good quality alkaline battery yields about 2,600 mAh at room temperature, so alkaline gives you about 1.4 times the the yield of 1800 mah Nmh. But drop the temperature to winter outdoor conditions and they easily become roughly equal, since the Nmh battery holds it's performance, while the Alkaline yields much less juice when cold. Thus, since you can recharge the Nmh about 900 times, and good alkaline or lithium batteries are expensive, you can save thousands of dollars using rechargeable cells!!

Shop around when you buy Nmh batteries. I recently bought a half dozen Powerex 1800mah cells from Thomas Distributing , at a good price. Buy your batteries in sets. When you receive them, divide into sets of your most commonly used number. For example, if you most often use sets of two in your radio and CD player, divide your cells into pairs. Mark your sets 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. Always, I mean ALWAYS use and charge your batteries in the same sets. If you must mix batteries from a set while charging, at the least be sure all batteries have a similar state of discharge. If you want details of battery tech, check this out.

It's also a good idea to occasionally test your sets of cells. Do so by pulling the cells out of your powered device when they've been run down and nearly discharged, but are still powering the device. Check each cell with a battery tester such as the Radio Shack 22-093. If any cell measures much lower than the others, discard it, and recombine the remaining cells into sets with other cells of the same vintage. 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 test (though some volt meters have a battery test function that does the same thing).

From the old days of Nicad battery use, you may be in the habit of trying to completely discharge your cells before recharge to prevent a problem known as "memory effect," wherein the cell would only charge to its last partial charge level, or something like that... This is not a factor with Nmh batteries. Indeed, you can ruin your batteries if you discharge them to rock bottom. Here's why: Consider a headlamp with two AA batteries. You leave it on until it goes completely black. No two batteries are exactly the same. Thus, at some point in the discharge of the headlamp one battery went completely down before the other. When this happens the fresher battery reverse charges the exhausted cell, and eventually ruins it. This is also why you use and charge batteries in sets. Doing so uses and abuses the same group of batteries in the same ways, so they'll always have similar charges.

Another note about discharge: Most sophisticated electronic gadgets, (such as 2-way radios,CD players and cell phones), have a low-voltage shutdown that protects your batteries from deep discharge. Be aware of how your equipment handles this, and act accordingly.

Okay, all that said, what's the best way to charge your precious little Nmh cells? First, consider the speed of charging. You'll see chargers that claim "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. Yet in my view, the "fast" or "one-hour" charge is so convenient it far outweighs the slight decrease in overall cell life. That said, if you choose to do fast charging buy a sophisticated charger that cuts off the charging at the correct time, and keeps the cells topped off for later use. I've searched far and wide for such chargers -- the best I've found for at home use is the Radio Shack 23-422 "Fast Charger," another highly recommended charger is the Maha MH-C204F, a four cell charger that's equally at home in your automobile as it is in your kitchen.

(Note: Using a trickle charger to preserve your rechargeable batteries might be wishful thinking. If your trickle charger has no cutoff circuit, and you forget to remove the cells, they'll sit there warm to the touch, being slowly cooked. Beware of cheapo chargers...and even expensive ones!)

All this is fine if you can plug a charger in at home, but what about traveling? If you can access residential type wall voltage, just bring your fast charger with you. They're small, and getting a charge in a few hours means you can re-juice in virtually any situation.

If you're a backcountry person who spends a lot of time away from home, at some point you'll wonder how to get a charge in your automobile, or at a hut with solar power. Here the key is using a slower "trickle" charger that works with a 12 volt feed (the most common voltage of solar power systems and autos). Rigging such a system can be as easy as buying the proper charger, but there are a few wrinkles.

The chief problem with 12 volt charging is that most (if not all) trickle chargers don't shut down. They continuously charge the cells at a low rate, thus wearing out the cells and placing unnecessary drain on your car battery or solar system. Also, if you place a battery backwards in the charger it can overheat and squirt nasty stuff out the small vent holes on the end. And there is a remote possibility that battery chargers can catch fire. The solution is to rig your in-vehicle charger with a small spring-wound timer, and mount it in a fire-proof container such as a metal box with correct ventilation. I cobbled together such a system. Here's how it went.

Setting up an in-vehicle AA battery charger

(Click here for parts list)

You need two key things for an effective in-vehicle charging system. First, the available chargers don't have a reliable shut-down circuit. This may drain your engine battery, may damage your AA cells, and could cause a fire. The solution is easy: just wire a spring-wound timer into the supply wire for the charger. Second, your charger and pricy batteries need protection, and you need protection from possible fire or over-heating since you'll be leaving the charger in your car unattended. Solution: mount all the components in a steel case. The idea is to have everything neatly mounted in a steel box, easily transported between vehicles, safe from mishaps -- with you and the interior of your car protected from damage.

For my mobile charging system I chose a Maha MH-C304F charger, a four cell fast charge unit, with a claimed shut-down circuit (if you need to charge eight cells, just buy two and wire together per this project). For a feed line, you'll want any of the variety of Radio Shack "Universal Power Cords" with an automotive lighter plug on one end, and a connector for a mini-plug on the other. Bring your Maha charger to the store, and the sales people can help you figure out the correct mini-plug and get the polarity right (e.g., which wire is positive and which is the ground -- if you don't know what that means, find an electronics nut to put this together for you). I got the Radio Shack power cord 270-1528D, which has an extra lead so I can power something else without needing a splitter.

1. The steel enclosure/case is the hardest part to find -- everything is plastic these days! I finally settled on an ancient first aid kit box I found in a junk store. It's a bit large, but is neatly divided into compartments I use to store extra batteries and accessories. I know...it looks crumby. I left it that way so it'll be less tempting to thieves when it's on the floor of my TAV (trailhead approach vehicle). Similar boxes are available from first-aid kit suppliers, and would work fine.
3. The timer was designed to mount in a standard residential wiring box, so I cut such a box to fit inside my steel case, then wired it in-line on the hot wire coming from the cigarette lighter adapter.
5. Next, I mounted the Maha charger in the case with adhesive velcro (so it's easy to remove).
6. I drilled a hole in the steel case, popped in a rubber wiring grommet, and snaked the feed-line through said hole.
8. For added nerd points, I mounted a small 12-volt fan over vent holes drilled near the charger to keep the batteries cooler while charging, and I drilled a few holes in the case over the charger indicator lights so they're visible when the charger is active. The fan might need an on/off switch or temperature control, since colder temperatures are bad for Nmh batteries while charging .
10. I cut and drilled chunks of styrofoam to make battery storage areas in the case (labeled for "charged" & "discharged"), and I drilled a few vent holes over the charger. The styrofoam storage is extra beneficial because Nmh batteries are sensitive to shock.
12. Last, I remembered that once in a while I'd want to charge batteries in a motel room. For wall voltage the Maha charger needs the "wall-wart" power supply it's sold with. But it seemed like a good idea to bring it while traveling, so I spliced a female cigarette lighter plug on the feed line so it will power my charger box, and I made a storage space in the box for the wall-wart and connector.

The Finished Project !