Battery test / load test

[coldcan]

I was reading another guys post where he's having trouble with his batteries dying after just a short time of use (its a '90 CC 36V, mine's an '87)), he was told to test each battery under a load, my question is; how do you put a load on a 6 volt battery one at a time when the motor is 36volt, plus I've read on here that you shouldn't run the motor without a load on it - can someone explain, I'm not having trouble with mine yet - but I'm sure I will ) (I'd be a little uncomfortable jacking up the rear end of that heavy sucker and flooring it, if it shook off the jack stands LOOK OUT ! ) Thanks !