All three batteries appear to have recovered. It started up tonight and everything seemed to work. I will let it continue to charge on shore power over night and then check the batteries with a multimeter. One of them seems to have a lot of gunk on the top.
What is the best way to test each house battery? I have read some conflicting info about having to separate them from the each other and the coach in order to test them. Is that true?
Completely unrelated problem: I was getting prepared to open up the dash to get to the chassis battery and found an unwelcome sight. The wood piece under the plastic dash covering and computer desk was just covered in mold!
Lots of fun. DW did an initial cleanup and bleaching of the area, but now we have to pull up the dash vinyl to see how far it extends under there. I assume that moisture is coming up from below, so I will need to seal it better. I'm glad I caught it.