What charges the house batteries

Thanks I just bought this motorhome it's class A I think I may need to replace the house battery's the lights worked inside but now they don't is there a switch on the dash that turns off these lights? There are switch's on the dash and I don't know what all of them do I downloaded an owners manual but it doesn't show the dash. I may have left a light on so were that drained the battery or it may be that the house battery's mat be weak. I have looked to try and find the house battery's but haven't found them yet. The very back of the MH has a door that needs a barrel type key that key I don't have so I will have to get that made then I can check back there. Luckily the engine door use's the same key but it's unlocked so I can get in there.