battery, charger or wiring issue?

The battery drains to nothing in just a few days when just sitting by itself with all 12 volt loads turned off (that can be turned off). I have also wondered about a mystery load draining the battery. The only remaining continuous DC loads should be the usual radio, propane detector, etc. No tank heaters or anything else like that.

I have a fancy $10 Harbor Freight multimeter that I just noticed will read up to 10 amps DC. Will see what I can read on each 12V circuit at the panel.

BFL13 wrote:
You have 12.4 at disconnected battery but when connected, no shore power, you get 11.1. So your rig has something "on" that is bringing the battery down to 11.1 as its "loaded voltage" from that mystery load.

There is no voltage drop unless there are amps on that wire, so that proves there is something "on"

When you plug in, the converter is able to handle whatever that load is and stay at 13.7

So what is the mystery load? One suspect is always the breakaway switch that leaves the trailer brakes drawing 12 amps when the pin is pulled on that. However that should also mean you can't move the trailer, so if this battery problem was going on when camping and you drove home then it should have been a tough pull!

Another is if you have heated water tanks and that is "on"

Maybe a short somewhere, likely on the tongue which is exposed to rain etc.

You could pull each fuse on your DC fuse panel, one at a time until the battery voltage jumps back to 12.x, which would identify the guilty circuit. Then you have to chase down what on that circuit is causing the draw. Say a wet lamp in the shower. But not everything that uses the battery is fused at that panel.