I wandered down to Cables and Connectors this afternoon looking for a battery tester. I had several dozen assorted batteries (mostly AA and 9V) hanging around. Between a difital camera, computer muse, guitar and bass pickups, wireless mic, flashlights - well, lots of places for batteries.
I have developed a bad habit of pulling them out of my camera (during balloon chasing, for example, or at kirtan), putting the dead ones in my pocket, and then dumping them out (on my bureau at night into one of my car cupholders, into my purse, or my cable tub). Of course, I also put a few fresh ones in my pocket, never use 'em, and dump them out into the same places. So I had piles of batteries and no idea which ones were fresh, which ones were dead and which ones were in between.
Cables and Connectors is closed on Sunday (make a note) but as I pulled out of the lot I though "dummy, you're an engineer...." - I own multimeters, and have boxes of parts, resistors, etc. So it took me about 2 minutes to cobble together a tester - with an 8 ohm resistor to load down the battery, and a meter. Quick work to check the batteries and sort them into categories: "new", "used but still good", and "dead". When I get some time I'll jot down the voltage levels that I found.
Dead ones in the recycle bag (take 'em to Whole Foods every so often) and fresh ones into various places - my music kit, opened battery packages, the camera case, and my laptop stand.