I am fortunate to have a reasonably well-stocked physics lab for my students. A number of the gizmos we use in the lab require batteries. Most of our battery-operated devices use the AA-cell.
A few years ago, I decided it would be worthwhile to invest in a lab set of rechargeable AA batteries.
Some people developed a distaste for rechargeables back in the 1970s when nickel-cadmium cells were used. Ni-cads had their issues, and they are disappearing from the rechargeable battery scene. They've been replaced by nickel metal hydride technology. NiMH batteries have enjoyed widespread adoption by digital camera users. They're good for hundreds of recharge cycles, and don't suffer the "memory" issues that NiCds were accused of having. They still check in with 1.2 volts (as opposed to the 1.5 volts of alkaline batteries), but I have yet to encounter that being a problem.
I use ten sets of four NiMH AAs and one eight-cell charger. The batteries and the charger get steady use throughout the year.
The current retail price of good rechargeable AAs is now less than $3 each ($10-$12 per set of four). Good alkalines run about $0.50 each. I'm happy with the performance of my NiMHs and I'm happy to not be filling the landfill with more and more discarded alkalines.
Buying advice? I've had good luck with Energizer and more recently Duracell. Look for high capacity values. As of this writing, I wouldn't go for anything less than 2500 mA h (milliamp-hours). Don't fall for fast recharge times--often that's how low-capacity batteries are marketed. Higher capacity batteries will serve longer between charges. And that's what's important.