Most motorhome that come with a residential fridge are newer models. There should be at least 2, if not 4, 6 volt batteries as well as an inverter of sufficient size to power the fridge. Since newer gas motorhomes are all on the Ford chassis these days, they are packing a 175 amp alternator which will have no trouble keeping up with the inverter draw. That said, I've run into so many people who don't even know how to turn on the inverter and just think they have to either plug in or run the genny to operate the fridge.