Short Answer: Sanyo Eneloop or Energizer Ultimate Lithium (depending on your application)
Long Answer: For performance, the brand of battery is not as important as the type. Nowadays, you have basically 5 different kinds of AA batteries on the market:
- Heavy Duty (carbon-zinc)
- Lithium (Energizer Ultimate, etc.)
- Ni-Mh Rechargeable
- Ni-Mh Rechargeable LSD (i.e.: Sanyo Eneloop, etc.)
- Heavy Duty (aka Carbon-Zinc) batteries are old-school tech from decades ago and have very poor shelf-life and low energy density. These can be very inexpensive, but you'll also get what you pay for. I don't recommend these at all.
- Alkalines have been the standard flashlight battery for many years. Most brands have pretty good performance and shelf-life. Any major brand should do a good job for you. The downside of alkalines is that they are only good for one use, so if you use your device(s) often, the cost factor can be high. They also don't like to be pushed very hard. If you have a demanding device, like a bright flashlight, it will start to dim fairly quickly because the cells cannot sustain a high current output throughout the life of the battery. According to Consumer Reports, most brands of alkaline batteries are of similar performance, though the more expensive Duracell Ultra brand does seem to have a slight edge in tests.
- Energizer Lithium cells, while more costly, have some significant advantages. First of all they are much lighter weight than alkaline. This can make a difference for backpackers. They also have higher energy density. A typical alkaline AA cell has a capacity of about 2,700mAh. An Energizer Ultimate Lithium AA cell has about 4,000mAh. In a flashlight, this might equate to 50?onger runtime. In a digital camera, the effect is more profound because lithiums handle high current better, giving you up to 8 or 9 times the number of pictures. This ability to handle higher current longer also means that a flashlight will maintain relatively consistent brightness for the life of the battery. Lithiums also operate better in cold temperatures. Finally, lithiums have a very long shelf life (up to 15 years or more), which makes them great for emergency lights, radios, etc, and they don't seem to leak acid like alkalines often do. Because of the high cost, I tend to only use lithiums in devices intended for emergency use, or where absolute runtime or light weight is essential. Just be sure to check if the device is lithium-compatible or you could damage it due to the higher 1.8 volt output.
- Another option is Ni-Mh rechargeable cells, which are my personal favorite. Overall, I think these are the best type of battery for flashlights, because they give you most of what is good about lithium batteries, but can be charged over and over again, potentially saving you alot of money. And if you get the LSD (low self discharge) type, such as Sanyo Eneloop, they'll maintain a long shelf life between charges (up to 3 years). As for capacity, standard Eneloop cells give you about 2,000mAh, the more expensive Eneloop XX cells give you 2,500mAh. Initial cost is about the same as lithiums (about $2-3 per cell), but can pay for themselves in only 5 to 10 charges. Ni-Mh cells will generally maintain a consistent output level over the life of the battery, so your flashlight will stay bright until the battery actually runs out of juice. Ni-Mh cells operate at a nominal voltage of 1.2 volts instead of 1.5 (alkaline) or 1.8 (lithium). This usually isn't a problem for most devices, because Ni-Mh doesn't exhibit as much voltage drop as alkaline. But it can sometimes result in a slightly dimmer flashlight. YMMV.
Hope that helps.
Answered By: flight777 - 12/22/2012