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

I have never been sure whether RV generator starter is connected to the house battery or chassis battery. If I shut off aux battery disconnect switch, and try to start generator, that should show whether generator is connected to house battery(s)or chassis battery shouldn't it?

BTW, I have noticed that generator will usually start using the start switch on generator itself, when it won't start from the switch at power panel.