Usually the house battery but some rv's use the chassis.
Seems kind of easy to find out. Without being plugged into shore power, why not remove the cables from the house battery and try to start the generator ?
You might have options:
Do you have shore power 24/hrs where you park it ? Leave it plugged in if you have a multi stage converter . Some systems like mine use the converter to charge the house and chassis batteries. My solar panel also charges both banks as well . Use a multi meter to test your system to see if they both charge.