On ours the dealer when they installed the batteries, they hooked up in series but failed to hook up in parallel. Facing the batteries. The 2 on the left read 6.5 volts each the 2 on the left read 5.3 volts each. The 5.3 v batteries. Were the ones they had the inverter hooked up to. The fully charged were hooked up to the converter. The dealers tech hooked them up at pdi and took hime 4 hrs. He didn't. Know what he was doing.
2011 Ford F-250 6.2l gas 373 rear end
2015 Cedar Creek 34RL