We bought a 2022 Interstate 19 in August, which only had a 50 watt panel to charge the chassis. From day 1 the chassis battery showed between 12v
and 12.5v, regardless of how much is was driven, and on a couple of occasions, after sitting for 5 - 10 days, Mercedes Me would give a "partially charged" warning. Both Mercedes and Airstream claimed there was nothing wrong, but since we don't drive the vehicle regularly, it made me a bit uneasy.
I finally decided to add an additional 50 watt panel, and the difference ever since has been night and day. The battery now always shows between 12.5v and 14.38v.
Even without a battery tester, I can look at the CZone Monitoring, and see the chassis voltage increase significantly (when there's some sun) between early morning and noon.