Which Battery is Best
by Bill Greer, Dallas Sierra Club Outings Chair
Most of us are increasingly taking our electronic gadgets with us on outings, and these gadgets all have one thing in common: batteries. Weight is usually a worry and replacements are hard to find in the woods so selecting the correct battery for the job is important. There are many choices, so which one is best? As with most engineering decisions the answer is "it depends." We’ll look at three types of battery: lithium, rechargeable nickel-metal hydride (NiMH), and the ubiquitous alkaline. All are readily available in the AA size so that’s what we’ll look at. Everything said here would apply just as well to other sizes except specific numbers would change.
Lithium The choices here are the Energizer "Ultimate Lithium" battery or "Advanced Lithium" battery. Except at very heavy loads the performance of these is very similar. "Ultimate" is more expensive than "Advanced." These batteries are attractive to backpackers due to light weight and claims that they "last up to 9X longer." There is no question that they are lighter than other batteries (14.5 grams vs. 23 grams for alkaline and 30 grams for NiMH) but do they really last 9 times as long? The answer is, again, "it depends." Under a very heavy 1 amp load they will indeed last longer than an alkaline battery. It’s more like 3 or 4 times than 9 times. But under very light load there is little performance difference between lithium and alkaline. Lithium batteries do perform much better at low temperatures than the other batteries. Lithium batteries are good down to -40°F. The others are good down to 0°F. Under a 1 amp load at 0°F the lithium AA may actually approach that "9X" advantage over an alkaline battery.
This battery is not rechargeable. When it’s dead it’s headed for the landfill. They can be stored unused for as long as 15 years. Cost is over $2 each. This is the lightest battery.
NiMH The big advantage of this battery is that it is rechargeable for hundreds of cycles. Take them out of your charger just before a trip and they are always fully charged and ready to go. When you come home with tired batteries charge them up and they’re ready to go again. Take a solar panel on your canoe trip and you can charge them up any time the sun shines. Freshly charged they deliver almost the same life as a new alkaline. Under heavy loads they will outlast an alkaline. If you have a battery hungry device and occasional access to a charger they will keep your devices humming without contributing nearly as much to the landfill.
I like a charger that charges each cell individually, such as the La Crosse LC-BC700 or the Powerex MH-C9000.
These batteries tend to slowly lose power when stored for very long (called self discharge) so they’re best used shortly after charging. Some versions offer lower self discharge but at the cost of slightly lower capacity. Cost varies widely but they can be found for around $2.50 each. When dead they are headed for your charger rather than the landfill! They are the heaviest of our three types.
Alkaline This battery is available everywhere in vast quantities at low cost. In low drain devices at room temperature there is little performance difference in life between an alkaline and lithium battery. It will probably outperform a NiMH battery in low drain service due to the NiMH tendency to self discharge. You’ll probably have to wait several months to notice very much difference. At high loads the amount of power an alkaline can deliver drops significantly. Our other two types will last nearly half as long under twice the load. With an alkaline it may be more like 1/3 or less.
They also tend to deliver that last part of their energy at lower voltage than the first part. Your headlamp will not be as bright at half charge as when the battery was fresh. The other two hold their voltage well and then fall off a cliff. While desirable, this characteristic can make it hard for devices to tell how much battery life they have left.
This battery is not rechargeable. When it’s dead it’s headed for the landfill. When stored for a long time they may leak and swell. They can be found for $0.60 each. Off brands can be found for less than half that and may perform almost as well. Weight is between lithium and NiMH.
Same is good Do not mix batteries of different types, age, or charge state. Bad things can happen if you put one used battery together with two fresh ones.
So which is best? Again, "it depends" on what you use it for. A battery that is best for one job may not be best for another. It may perform OK but cost too much. Let’s look at a few cases:
Backpacking headlamp: There’s no clear winner here. I prefer the lithium battery for long trips due to the small performance advantage and big weight advantage. When you’re talking about a trip to Wyoming a few dollars extra for batteries doesn’t amount to much. For weekend trips I use NiMH. With a fresh charge these will last several days.
Cold weather Lithium is the clear winner here. In cold conditions they deliver a lot more power than anything else. They’re good down to 40 degrees below zero. If it ever gets that cold I’m not going to worry much about my batteries. According the Energizer data sheets there is little difference between energy delivery for a lithium battery at 32°F and at room temperature. An alkaline battery may give you half as much power or less in the cold as it did at room temperature. If you’re going on the Taos trip you want lithium batteries.
Frequently used devices If you have a device that needs fresh batteries often (a kid’s game for example) you want a set of NiMH batteries and a charger. You’ll always have fresh batteries and won’t contribute as much to the landfill. After 5 or 6 cycles the cost difference will have been recovered.
General purposes If you have a device that is used infrequently and doesn’t place a huge load on its batteries you’re probably better off with alkaline. Don’t leave them in a device for years or they may leak and ruin it.
More info than you probably want:
Ultimate Lithium: http://data.energizer.com/PDFs/l91.pdf
Advanced Lithium: http://data.energizer.com/PDFs/ea91.PDF
engineering guide: http://data.energizer.com/