La Mesa dealers are consistently useless - their service departments are generally incompetent.
Have you talked to the factory? If not, call and ask for Sean Heinz. He is the manager of warranty and service and has been extremely helpful working with some of the poor dealers, or perhaps he can send you to one of the known competent mechanics in California who can deal with these systems. (of which there are about 3, but none are dealers)
It seems that your underhood generator (2nd alternator) is not charging the batteries. Since they said that they replaced it, perhaps the Balmar (controller) is bad or set wrong. I would suggest calling Nations Starter in Missouri and they can help your husband troubleshoot.
2021 Promaster 1500 118wb conversion
2019 Roadtrek Simplicity SRT (almost a Zion)
2015 Roadtrek 170
2011 LTV Libero
2004 GWV Classic Supreme