Originally Posted by Byron Kinnaman
If the trailer battery has a shorted cell, it could cause this kind of a problem. We're still not sure what battery was new, the one in tow, or the one in the trailer.
If the trailer battery was not replaced I sure would suspect that it has a shorted cell.
Shorted cell it could be but if so the trailer battery would die rapidly even if charged by battery charger but not connected at trailer plug. Sediment can do a "slow" short in a deep cycle batt that would make the battery a heavy drain if connected to tow.
I was shooting for elimination, if trailer batt. dies with trailer not plugged in problem is trailer specific because car trailer plug and wiring is not in the picture.
I would then disconnect trailer batt and test. But I have meter, hydometer and charger so not a big deal. Or I would take it into the battery shop.
Simple test sequence for folks without test equipment is:
Charge battery. Make sure fridge is off at the propane/110/12 volt switch and see if batt can run trailer inside lights
for a couple of minutes. If it won't run the 12 volt lights
or they rapidly dim even after batt. is charged it's a bad battery.
If it will run the lights
, disconnect batt. and reconnnect next day to see if it will run lights after sitting overnight. No? Bad battery, probably with a short that killed it even when not connected.
If however the trailer battery will still run the lights the next day, turn lights off and leave connected. Check back in a couple of hours and see if being connected to the trailer 12 volt system kills it.
If it does die from being connected to trailer then there is a short or something like fridge or an inverter is drawing power even when off. Time to start disconnecting stuff or get a meter to track down the line that is drawing the juice.
If trailer battery connected to trailer overnight or through the day does not die then it's something with the tow and it's plug. But as described tow battery dies ONLY if plugged into trailer.
That would either be a draw in the trailer wired directly to the trailer plug or some sort of short in the plug or it's wires on the car.
I would as others have mentioned expect a burning smell or melted wires for tow or plug short but have seen shorts from oil or across damp wires that did draw but did not get hot enough to melt. Still 15 minutes to dead battery is a really big draw, headlights won't kill it that fast typically.