Invertors are usually the culprit. Make sure it is powered off. Even with no load it still uses power.
Class a's also usually have a bi directional relay that will tie both chassis and house battery together depending where the charge is coming from. Sometimes it gets confused and doesn't release
My class c has a time delay that only operates with engine charge. I have never (knock wood) have both discharge and leave coach unplugged for up to a month.
__________________
|