Dean -
If you left the battery connected over the winter, then the phantom loads (aka parasitic loads) in the trailer completely discharged the battery. Not a partial discharge, but right down to ZERO. Complete discharge is very bad for a battery, and that in itself may have destroyed it. Beyond that, a battery that is completely discharged will freeze at about the same temp as plain water. Freezing almost always destroys a battery. Was the TM stored where freezing temps were encountered? If so, everything you have done since simply confirms that the battery needs to be replaced.
You can do a SEARCH of this board for "parasitic loads" or "phantom loads" to find more information on this topic.
On the other hand, there is an outside chance that there is a different problem. The symptoms you describe are kind of ambiguous.
First, if you plug the TM into shore power, then the interior lights should light. If the lights don't light while the converter is running, then possibly the converter is bad. Or, for some reason, the fuse in the light circuit has blown (this is unlikely, IMHO).
If the lights work, the next thing to check is the battery fuse. This is a 30-amp fuse in the main battery line (red wire, about 6" away from the battery). If the lights work, but battery doesn't charge, then the fuse MAY (repeat MAY) be bad.
HOWEVER:
If you connected your portable charger directly to the battery (portable chargers usually have battery post clips), and the battery still reads 11.88 volts, then your battery is gone. The main fuse is not part of this situation.
How old is the battery? If it is the original battery, it is now 8 years old, it is WAY overdue for replacement anyway. I generally figure 4 years is about as long as a battery should last.
Putting all of it together says that you need to replace the battery. Sorry.
Bill
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