I own a 2013 Thor Citation 24SA with the coach batteries in the compartment beneath the stairs. For the past few months, they have been giving me fits and I finally resolved my issue. I found the problem by piecing together information from various threads on this forum. And as you already know, most all of these rigs are put together differently and whats good for someone may not work for another. Anyway, here is my solution in the hopes it helps someone else who has the same problem down the road.
I replaced my coach batteries recently but for the life of me, I couldn't get them to work. The battery disconnect switch would not activate and nothing worked on battery power. However, both the shore power and the generator power worked fine. I checked the batteries and they were fully charged. I checked the fuse box and the GFI in the bathroom but nothing was wrong there.
From the Thor forums, it seems most people were saying there is a small breaker button in the bay with the batteries. Unfortunately, I had nothing like that in my battery bay. I did find one post where someone had found the inverter mounted behind the fuse box under the stove. I removed the bottom drawer that was above the fuse panel.
Once I got that open, this is what I saw.
Now, in the bottom left portion of this picture, you can see battery wires mounted to little gray plastic boxes. One wire has a yellow connector and the other a blue. Thanks to a forum user who posted a pic of these boxes on another thread, as I would have had ZERO clue that there is a small reset switch located on one of these boxes. The box on the far right (with the blue connector) had a small black plastic button sticking out of the top. If you look real close in the picture above, you can barely see it in between the blue and yellow connectors. Here is a better photo of the switch. The arrow is pointing directly to the button.
Just give that button a push and you should be able to use your coach batteries. Just keep in mind, these boxes could be located in a different location on your rig, but at least now you know what to look for. Good luck!