Interesting: The circuit board in the storage compartment under the drivers seat is setup to charge both batteries when plugged in (it uses a couple of diodes to provide a charge to each battery and prevent them from discharging). You can see the diodes in the circuit diagram I posted in this thread:
http://www.thorforums.com/forums/f8/...-box-1203.html
At any rate that circuit board is the first place I'd look.
BTW: We just returned from a 9 day camping trip with no such issues (plugged in the entire time).
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