You said you never checked the batteries in 17 months ?? Dis you ever think they mite have ran dry.
Heres a fact,.......
If you store the MH w/o any power to it, the batteries must be disconnected, either thru a disconnect switch, or removing a battery cable. If not, the batteries will be dead in 2 weeks
Another few facts,........
If your batteries ever get stone dead, and set for a month, thay are junk.
And if they go stone dead more than twice for even a short time, they are probably junk.
Batteries have to stay full charged whenever not being used, or they will be short lived.
And if they ever run out of water while charging, they will be junk.
You should read "12v Side of Life"