ShapeShifter said:No, it should be powered all the time.
Yeah, I would suppose that the trailer could back-feed the truck and drain the battery.
I would think that some kind of heavy duty rectifier should be on the trailer where the wire attaches to the battery so that it will allow power to flow into the trailer on that wire, but not back out. I would think that this would be a common problem, and such a part would be easy to find. Isn't there some sort of battery charger controller on the trailer? I would think that one of its functions would be to prevent that from happening.
Another think to check is for dirt/corrosion on the trailer battery, or somewhere in the wiring that could be causing a current leak to ground. Also check for any parasitic current draws in the trailer (accessories that are left on and always drawing power.)
Finally, it could just be that the battery is failing, so that it just can't take much of a charge or hold it for very long.
-- SS
I know the battery is good, because it does not loose juice until it is attached to the truck. If I charge it, and tow without hooking the wiring harness to the truck (short distance drive) I do not have the problem and the battery lasts all weekend. But attach it to the AV and it dies fast. I will look into your other instructions.