[JRTJH]

There are two 12 volt "automatic reset circuit breakers" mounted on the bulkhead at the front of your trailer (between the A-frame members). My guess is that one of them is corroded and no longer allowing the charge voltage to get to the battery cables.

You'll probably need to remove your propane tanks to get access to the area, unless you can lay on a creeper and slide under the A-frame.

If you decide to take them off, TAKE A PHOTO before you start disconnecting them. It's very easy (far too easy) to get them "miswired" on reconnection.

On some trailers, the mini-breakers are inside the front passthrough, but usually they are on the bulkhead.

Here's what you're looking for on the bulkhead. There will probably be a red plastic cover over the terminals.