what battery is used for starting a generator in a class C

I am too late! Glad you found the problem. I was just about to mention the battery disconnect switch for the coach batteries. When my switch is in the off position, and I try to turn on the generator, it sounds like the coach batteries are dead..until I click on the switch. With the switch off, the engine battery will not start the generator, even with the assist switch, at least on mine, a 2008 Tioga.