Typically you have house batteries and chassis batteries. House batteries for interior lights, refrigerator, furnace, water pump, etc. Chassis batteries control driving functions. Sounds like your house batteries are not connected, but I'm not clear when you say, "Replace both 6 volt batteries. 12 volts was ok." Near the entrance there is usually a battery disconnect switch that controls a solenoid that shuts off house batteries for storage. Is that on? You might have to trace the power from the batteries to the converter/charger to be sure everything is operating. There is often a large, 80 amp fuse in the cable from the batteries for safety.