Don I went from two 12 volts up to two 6 volts batteries. You will get from 360 -440 amps/hours out of the two 6 volts, and only 140 -170 amp/hours from two 12 volt batteries. As far as weight the 6 volt weigh 122 lbs and 12 volts weight 106 lbs. I'm sure you know one will wire in parallel (12volts) the other series (6volts). Found this imformation at
http://www.marxrv.com/12volt/12volt.htm I'd bet the two 6 volts would cost less?