Low Battery on my Winnebago Adventurer

My chassis battery won’t start! My battery boost also will not help start the engine, I push the battery boost switch to on position and I have no response. My chassis battery is dead and both my house batteries are reading 13.8! I do hear some clicking from the solenoid and when the keys are in the ingintion and I play with the keys I do at times get idiot lights. There is a sticker near my batteries saying disconnect batteries before charging, does this mean turn my battery control switch off are actually disconnecting the positive cables on all 3 batteries? And what is the reason for doing this? I currently am running my gen set to get house batteries charging at 14.0 to 14.2! If running the gen set don’t help then I’m going to take my chassis battery into town to get it checked out. Thanks, John “Rooster”