Fuse blowing

[ctfisher]

I apologize ahead of time if this or a similar question has been addressed in another post, I'm still making my way around the forums.

My problem is with a 2012 Outback 279RB

Basically, I put two batteries in-line to extend the amount of time the furnace will last during cold weather. This worked for quite a while, and we're running off of a generator.

I took one home and fully charged it because it seemed like the generator didn't quite charge the pair up full, then brought it back and put it back inline the way it was before (or at least I think I did).

Problems that occurred at this point: Most bulbs in the trailer ran really bright then blew out. The car charger type charging port under the tv/next to the stereo head stopped working. The awning stopped working.

I pulled the second battery and everything went back to normal. We've replaced the bulbs and it all looks ok.

There is a fuse that is blown and has a red light next to it. I've tried replacing it, but the new fuse blows as fast as it touches the connectors. I've disconnected the charging port fitting altogether to make sure it's not shorted, same result. I also pulled the control button for the awning thinking it had melted inside, but the fuse still pops immediately.

I'm open to any and all ideas/suggestions to try before I kneejerk and pick up a new fuse panel/control board.

Thanks in advance.

[travelin texans]

Sounds like you wired to 24 volts. The 2 should be wired positive to positive, negative to negative. Unfortunately there's any number of 12 volt items that are possibly damaged by 24 volts, fridge/furnace control boards, water heater to name a couple.
Also it's best the combine identically matched & same age batteries. The older weaker one will keep draining the stronger newer one, not the other way.

[ctfisher]

Yeah, I'm thinking you're right. I'm probably lucky these are the only two things I have to repair.