When running the engine both house and chassis batteries are charged.
Depends on the RV. On my 1990 Winnebago Warrior, there is a 2-way switch on the dash. In order to charge the house battery from the engine, this switch must be engaged to the left. Also you must not engage it while the engine is running
and the generator is running, or you will destroy the competing voltage regulators.
If the switch is flipped to the
right, it gangs the house battery to the chassis battery for emergency start situations. It is momentary to the right and releases when you let go.
Steve