I believe "STB" = "Poop" The Bed (substitute Poop for it's censored equivalent) LOL
Coelacanth, you said he replaced the inverter and noticed his batteries weren't charging then. Is it possible he originally had an Inverter/Converter and he replaced it with just an Inverter? The Inverter turns the 12 VDC to 120VAC. The Converter takes 120VAC shorepower (or generator) and converts it to 12 VDC which charges the house batteries. The coach battery may or may not be charged from the Converter. If he replaced an inverter/converter (sometimes called inverter/charger) with a straight inverter, that's why his batteries are not charging when he is plugged in to shore power.
Good Luck,
~Rick