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

You are right it is the coach batteries that drive the generator starter. I pulled the batteries and one of the connection had some green corrission on it. The water levels where good and the acid levels. Cleaned all the connectors and coated with silcone grease to hopefully keep corrission to minimum. The generator fired right up after that. I do like the idea of running the engine while starting the generator so you have that extra voltage. Thanks for all the great ideas and help. Problem solved!