My random thoughts on batteries:

I get my generic AA alkalines for 25¢. I wait until I see sales. These have about a 5% lower capacity than Duracell who are 2-3x more expensive. Except there is one generic brand that is terrible: Stay away from batteries.com. I wonder if they aren’t really selling carbon-zinc batteries (disguised as alkaline).
I get my Energizer lithium AA from Sam’s club for $1.67 each. I tried the generic lithium’s on the internet for $1.00. I thought “wow. Good price.” But they only go for ½ as long as the Energizer Lithium.

I’ve tested Sanyo, Kodak, Energizer, and Duracell 2500mAH NiMh AA batteries. Kodak has lasted the longest by taking the most charges (approaching 250 on my count) and they last the longest (per charge) of all 4 brands in my flashlight.

I use my Fenix L1D flashlight every day of my life (biking, backpacking, work). On high, the lithium AND the NiMh go for 140 minutes (stay bright before dimming). Yes, both get the same time (maybe Lithium gets 2 minutes more). You can see how the rechargeables save money. I only use the Lithium backpacking since they are lighter. I use the NiMh for all other times; that is an incredible money savings.

Rechargeables are great for flashlights that hold a constant output (like Fenix). 3-Cell lights tend to do poorly with rechargeables (compared to lithiums) because they rely on the battery voltage more than the energy left (like a Fenix). Again, out backpacking, I use Lithium to save weight and it does better than NiMh in colder weather. You would have to take four alkalines to equal the runtime for one lithium. That’s too much extra weight and bulk. Plus alkalines do extremely poor in cold.

If I was only using my flashlight once/week, I would switch back to Lithium’s since NiMh still have a higher self-discharge rate and who wants to be caught w/ a dead battery?

For cold weather, NiCd is the best, followed by Lithium and then NiMh. Alkalines--- just don’t take them!

Now if we could just get a 2500mAHr AA NiCd (1000mAHr max today), we would have an awesome runtime rechargeable for all temperatures.

Some GPS’s have a battery software switch to let you switch between rechargeable and alkaline. This way the battery warning doesn’t come on too soon.

If using NiMh, make sure your charger has –dV/dT technology. This will shove a constant current through your battery. The battery will then hit somewhere between 1.38 and 1.42V and then start dropping (even though constant current is being applied). When the battery dips, the charger will then completely cut off the current (no trickle charging allowed for NiMh or their life is cut). The faster chargers will also monitor temperature so they can crank up the current w/o killing the battery.

Another type of charging that Toyota Prius uses is: just charge it to 90% capacity. In theory the battery will last forever. I’m still testing this and I’m at 192,471 miles; and so far--- they’re right.

Any other type of charger will shorten the # of charges your NiMh can take.

-Barry