As I've mentioned before, I'm a fan of not burning through single-use batteries. And we have plenty of need for batteries in the physics lab.
I've been using nickel-metal hydride (NiMH) rechargeable batteries for my AA needs for several years now. More recently, I switched to NiMH AAAs, too.
The trouble with NiMH batteries is that they discharge when not in use; they don't have much shelf life when charged. And the first thing you do with new NiMH batteries is to charge them.
Upon a recent visit to www.greenbatteries.com, I noticed something new. (New to me, anyway.) Ultra-Low Self-Discharge (ULSD) rechargeables. They're NiMH batteries that ship charged because they retain their charge when not in use. Rechargeables with shelf life. The compromise is that ULSD batteries have lower charge capacity: 2000 mAh rather than 2400-2700 mAh, the current state-of-the-art for high-capacity NiMH AAs.
With the assistance of our Rio Americano Science Boosters, I've been able to outfit my lab with AAs and AAAs. I also got a set of high-capacity NiMH C-cell batteries for our constant-velocity buggies and circuit labs.
As far as I know, my only need for single-use batteries is the occasional button battery or 9-V. Thank you, Science Boosters!
In other rechargeable battery news: nickel-zinc (NiZn) batteries are coming online. While NiMH batteries operate on a 1.2-volt reaction, the nickel-zinc reaction provides 1.6 volts. (Single-use alkaline cells yield 1.5 volts.)