No 12 V power at all W/O shore line or generator

my rig is 2003 Fleetwood southwind.


I just timed it, when I shut generator off 12v power lasted 2 minutes lights went dim at 2mins then all power was lost at 2 mins 5 secs.

when all power goes, I have to start engine on truck to even start generator. Where does power to start generator come from???
Coach batteries or truck battery??