Take them to Autozone or Advance and have them check them all. They have the machines to do it. The weakest one loses. My experience is that Autozone just uses the harbor freight "load tester" battery tester. Adcance hooks them up to a computerized machine and runs them through for about 30 minutes trying to charge and what not. Not sure which one is better, but I've had one say it was good and the other say it wasn't, just don't remember which one...

I have saved a few batteries that the chargers wouldn't charge by hooking the weak battery to a good battery with jumper cables and then charging the two together. It tricks the charger into believing the one with 8v really has 12+ and brings it back. Did that with an optima a week or so ago.