[Richard]

First, do some diagnostics to ensure that the inverter charger is the problem.

What are the voltages on the batteries with the charger turned off? and with the charger turned on? I cannot help you without those readings.

What does the charger panel show as output when the charger is enabled? I am curious if it shows any amps going out of the charger.

It would be a good investment of time to study the manual to ensure you know how the unit is supposed to function.

I appreciate the urgency because the Frau is cold, but you may be throwing money at situation that won't fix it because something else is amiss.

Stop merging the batteries while parked. Your Aquahot is using 12V power that is not going through the inverter. You have NO protection against the AH completely killing your batteries. I would expect to replace both the house and the chassis batteries after drawing them to low voltages twice.

I have the Magnum 2812, tons of adjustability, and capability to add auto gen start, solar. Installing a new inverter in place of the Heart is not a trivial task.