I have a 2014 Winnebago sightseer. Chassis battery is only a year old and fluids are full. I have shore power(50amp) plugged in. However, if I leave unit unattended for a period of time(Still plugged...
Ok, Many RVs the house converter or charger also charges the chassis battery.. Same as the Engine alternator charges both chassis and house via the isolator.
However MANY =NOT= ALL. yours may be one of the "Rest" as it were
IF you are supposed to have a bi-Directional isolator.. IT's not working