Our 2017 Gemini has about 15,000 miles on it, 8000 since we picked it up used, and our coach batteries no longer seem to be able to hold a charge. They charge up full from AC, from the engine battery, and from the generator, but turn off the charging source and they drop back to near-empty within a minute or two.
Is this the normal lifetime? Do I need to replace them? Anything special I need to know about them?
Extra Credit: Is this situation a threat to any of the systems, such as the on-demand hot water heater? Does it need a spark or something, or does anything require continuous current? Reason I ask is, when I first come aboard after the battery has been discharged for a while, I hear an alarm or a beep from the back of the coach. I assumed this was the water heater telling me it needed LPG, but maybe it needs a current also? I just don't want any explosions in my driveway, thank you.