Check the voltage to both batteries, coach and engine. One might not be charging. ..
I found this problem while at a air show in San Diego. The drive home should have fully charged my batteries, but it did not. Normally I might expect the battery to be depleted after a long weekend of camping, but this one day trip, I did not expect it to be depleted at all, with the 20 amps of solar keeping it full. On the way home, I did not expect it to be discharged. Anyway it was the time that I discovered that the engine to coach battery relay was bad, and I installed a new one myself.
Good luck,
Fred.