Chassis not charging coach batteries, need some help with diagnostics

[Jdmalibu]

Hello, I have a 2007 Sunova 35J

The Coach batteries are 1.5 years old, and have only used the coach about four trips.

The deep cell batteries after charging with a charger read out as only 8.8 on the multimeter, while the chassis battery reads a full 13.

When the chassis is running, I still get the same low reading on the house units, but slightly higher on the chassis battery.

Shouldn’t I be getting a charging flow from the chassis lines on the coach batteries while the truck is running?

I’m just not sure if I should buy new batteries, or is there another issue with the charging system.

My next step is to check the battery fluid level, and try to charge each one independently with a charger.

Any thoughts on how to diagnose the chassis charging system for coach batteries?

Any help would be appreciated.

Thanks

Jon