Elliot.........I am not familiar with how Marathon hsa set up their conversion, but nothing I do inside my coach, lights, radio, etc. has anything to do with the chassis batteries.

If I turn on the coach headlights or light lights in the engine area I use chassis power, but even my bay lights are on the house batteries.

My inverters are always charging my house batteries except when we are driving or dry camping, but I don't have any confidence in any battery charger to protect chassis batteries. Too many stories about cooked batteries so if I do extensive work on the chassis using chassis battery power I turn on the charger for a few hours and then leave it off.