OK, so you just got back from a dive, dumped your gear in the bathtub, and head out to get a beer.
Your batteries are in various states of disarray - so which ones have a full charge,and which ones need charging? Doh! You don't want to put a drained set into your camera and have it die in the middle of your next dive...
It would be easy if you could put them all in your charger, but they don't all fit. Hmm... It's easy if you only have one set of batteries, but what if you and your dive buddy have 4 or five sets???
Well, here's a super easy and pretty "aggie" way to manage it. Use a big ziplock bag and a small ziplock bag. I just keep all my batteries in the big bag. Any batteries that are not fully charged go into the smaller bag inside the big bag. As they get charged, they move to the "pool" of charged batteries. That way I can just grab four (or 8) of them out of the pool and I know they are good. It also helps if you have the same mAh rating for all of your batteries. You shouldn't mix them!
HTH
James