So my coach has 4 8D house batteries (12V is parallel) plus 4 engine starting batteries (series/parallel creating 24V) plus a 12V battery dedicated to my generator. None of these batteries are interconnected in any way. It's just important to understand what you have an how they do or do not interact. I have a 24V alternator and a 12V alternator for the engine/house batteries plus a 12V alternator on the generator to keep that battery charged. Is this normal? Nope! Is that what I have and what I need to understand and maintain? You bet 'ya!