I purchased a 2016 Thor Majestic 23a in December and all was well until this week. From Dec-May I was hooked up to shore power 24/7 and everything worked. I recently took a cross country trip and didn't have any problems. The RV was unplugged from shore power and in storage for 2 weeks and now the chassis battery is completely dead. I installed a new radio before the trip and assumed it put some parasitic drain on the battery. It is a previous rental unit and doesn't have a storage/isolate switch, but it does have an emergency start button.
I used this and the RV started. After starting the RV I used a volt meter and the chassis battery was at 18V! I turned the RV off and sure enough the house battery is at 18V.
My initial though is it is a bad converter (WFCO 8955) overcharging the house battery. After googling I found info stating a bad battery can cause a converter to overcharge a battery. To add to my confusion the chassis battery is out of the RV and the emergency start switch is not depressed, but the door lights, dash lights, and radio are working.
Is this normal? When the dead chassis battery was connected I had no power to the dash lights or door locks. I thought there was a relay or solenoid that connects the house battery to the chassis battery when pressed.
The house battery is AGM and the chassis battery is a Motorcraft, both have dates from 2020. I had the Motorcraft battery tested and its dead and won't accept a charge. I know I have to replace the chassis battery, but any tips on troubleshooting or normal charging operation would be greatly appreciated!