I read your post that you checked the battery voltage "at the battery."
If not then you must.
There are two fuses (current limiters) between converter and the battery. If one of them opened, you would see converter/truck voltage all over the coach; but not AT the battery.
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW