Cabin batteries generator charging system ? How long?

by Orie
(Tucson)

We dry camp some, we would like to know the cabin battery charging rate when running the generator. I know that we need to charge the cabin batteries almost every day but I have no idea how long I need to run the generator.

I don't even know if the generator has a 12 volt output connected to the batteries of if there is a rectifier charger system. I was supplied a large amount of manuals but it seems like every thing I want to know is not in the manuals.