2 - 6 volt batteries or 2 - 12 volt batteries or...

How old are the batteries that are dead? When was the last time they had life in them? I've resurrected a completely dead car battery (sat for over a year dead) -one my smart charger wouldn't charge but my dumb charger would get something going after a few days on it. Then an equalization from the smart charger. It may have been damaged but it was enough to continue to start the car.

I agree-once battery is solved find a way of maintaining it...