After a long drive to the trailhead, you’ve tossed your last items into your pack, drained the last drop of coffee, and locked the car. On the skin out of the snow-covered parking lot, you kick out ahead of your buddies for a group beacon check. Yesterday, you toured resort sidecountry, and your beacon was still registering above 90% battery life. With the flick of a switch, you turn your beacon on. Oh, oh no – dead batteries!? How!? After a fraught few minutes fruitlessly searching for spare batteries, and hours from the nearest gas station, you reluctantly agree to wait for your buddies to return rather than risk being in avalanche terrain with a dead avalanche beacon.
Battery Science
Two main types of AA or AAA batteries are on offer in today’s marketplace: alkaline batteries (cheaper) and lithium batteries (more expensive).
Lithium batteries are rightfully known to be superior to alkaline batteries. They have a lower self-discharge (longer shelf-life), more consistent power output, and function much better in cold conditions than their alkaline counterparts. Lithium batteries are an ideal choice for a wireless computer mouse or noise-cancelling headphones. That said, lithium batteries are a travel-restricted item. While it’s not common, they can discharge unexpected causing sparking – not ideal for an airplane hold, for example!
Alkaline batteries, an older style, simply aren’t as efficient as lithium batteries. First, they don’t have as long a burn-time as lithium batteries.
Second, they gradually drop in voltage output over their lifespan (less power output). Lastly, the reactions taking place to produce power within an alkaline battery measurably decrease in efficiency over their lifespan. Scientists call this last drop in efficiency “internal resistance”. A side note, here: internal resistance in a battery, which effects it’s performance, can fluctuate significantly with temperature.
Beacon Batteries
In the opening example, the problem experienced was, counter-intuitively, the incorrect use of lithium batteries. While lithium batteries can be superior to alkaline batteries in many ways, most avalanche beacons are designed for use with alkaline batteries.
The battery-reading circuitry installed in most avalanche beacons depends on the decreasing voltage output curve of an alkaline battery to give the user an accurate reading of the remaining battery life. Thus, it’s possible to have your beacon read 90% battery – and then unexpectedly drop to 0% battery without much warning.
When we’re talking about a wireless computer mouse at the office or at home, a fairly sudden battery death isn’t life-or-death. For most, spare batteries are easy to ferret out of a desk drawer, pantry, or basement. At worst, batteries are usually available within an easy striking distance of the dead device. They payoff from using a lithium battery is usually worth the suddenly immobile mouse-cursor, since it can buy weeks more time than using alkaline batteries.
In the wintry backcountry, perhaps situated high on top of a peak and about to drop into a skier’s powdery dream, reliable avalanche beacon batteries are a completely different story. Unless you are using one of a very few 
specially built avalanche beacons which work well with both battery types, stick to tried-and-true alkaline batteries for your avalanche beacon. Lucky enough to have a beacon that accepts both lithium and alkaline batteries? Go lithium, and be sure to toggle the settings on your beacon so it will properly read your lithium battery life.
Rechargeable Batteries
Rechargeable batteries are a flat-out no-go for avalanche beacons. It’s possible that various brands like Mammut will eventually offer an avalanche beacon with a factory-sealed rechargeable cell, but until that day do not rely on rechargeable AA batteries. Rechargeables are much more volatile, with a greater chance of discharge, lower opening voltage performance, and an overall lifespan issue.
Battery Storage
When your avalanche beacon batteries are “off duty”, remember to store them outside of your avalanche beacon. This will prolong their lifespan and help protect your beacon from accidentally being switched on or your batteries from discharging within your beacon. Always double-check your beacon’s battery life before driving to meet your ski partners, and always bring a set of spare batteries at least to the final moment before you leave the car or resort. You might save not only your own ski day, but your partner’s, too!
