Mihand
It's possible you have a combination charger/ inverter
The control panel will say inverter
This is two sets of electronics in one box
The 13 volt battery charge side will only work when 120 vac is present
To work without 120v
The batteries have to be connected and in good shape, to have the 12v lights and systems working
The inverter output 120v side will be connected to the entertainment systems and maybe the kitchen outlets
Only one side can work at a time, it does not invert aka make 120v unless the batteries are connected and charged
It does not charge unless you have a120v source
The house 12v systems must be connected to the CHARGED batteries if there is no shore or generator power
