First of all, I have to say that what I have heard from other Thor owners is the fact that they do some strange (non standard?) things with their designs at times.
So, my comments here reflect what I know about the industry electrical systems as a whole.
With that said, I can say that when the walls of an RV battery "sucks in" there has been a serious Short internal to the battery itself. Usually this happens when the plates inside the battery actually touch each other.
This can be caused by having a load on the battery and allowing it to get hot and boil the water out of the battery.
So, considering your symptoms, I recommend that you use a multimeter and measure the voltage across the battery terminals. An RV battery should have a voltage of around 14.5 VDC across the terminals when it is being charged, and not over this number. As the battery takes a charge, this voltage across the terminals will drop to around 13.5-VDC which indicates it is fully charged.
This charging voltage is provided by your built-in CONVERTER. If this charging voltage is suspect, you may have to check out the Converter.