For Rick: The wire that keeps the battery charged was & still is, fused. Large white wires are not, but are short and in the open with nothing to rub on. Battery is tied in place by zip-ties (where would technology be without those marvelous things? Baling wire or duck tape just looks so shoddy.) Of course, the cig plug on the 500 has its own internal fuse.

Ted: The low voltage fault may well be a bad wire or sensor. I think you're on the right track to replace or swap those as the first step. If that doesn't fix it, I'd take a close look at the batteries. Maybe hook up a scope and see if the pure, smooth DC that's supposed to be there, really is.