It's not an obscure issue - hundreds of posts on this Forum alone about similar issues.
Step 1 - Go to the Thor Owners Resource login page ans create an account with your VIN:
https://www.thormotorcoach.com/owners
Step 2 - Download appropriate documents for your RV to determine if you have a Bi-directional Isolation Relay Disconnect (BIRD), Battery Isolation Monitor (BIM), or Isolator Relay Delay (IRD) IRD.
Step 3 - Determine if your coach is supposed to charge the house batteries from the alternator.
Step 4 - Commence troubleshooting if required.
Thor Forums
