Not sure what forum... Just got a NTU camper. Got it home and checked the battery; -4V. Huh? I expected flat but not negative. (And yes, I know how to use a multimeter!) no date of purchase, and the prior owner said it was at least four years old, and I suspect it's been drained a few times--so I plan to just replace. But any idea if it can go negative? I haven't checked on the charging wires, for some odd reason they used a black wire and a green wire. Will look at manual later.