Just a bit off topic: my cameras use batteries from alkaline button cells to specialized lithiums. There's also a bunch of stuff in the house that uses AA batteries. A really, really nice battery tester is one of these made by ZTS: http://www.ztsinc.com/mbt1.html
It tests just about every kind and formulation of battery available. It also tests under load for accuracy, not just the voltage so you'll know exactly what's left in the battery. It's really, really useful for the above mentioned specialty batteries so there's no second guessing when the battery in my RZ needs replacing, the AA in my hand held light meter is weak or even if I need to change the button cells in the red light for my telescope.