Follow-Up:
I would try removing and charging these units.When the battery is totaly dead they will appear shorted.Also test machines at auto parts places will show them as bad.I have replaced mine but kept the old ones only to discover after charging them for a couple of days each, they then tested good at the same place that said they were shot.Ive stored the old batteries outside through the past winter here in connecticut and they seem to be maintaining their charge.Rember it takes a couple of days to get a good charge on a deep cycle battery.