Coach Batteries Charging Solenoid Issue
I have the same problem: running the refrigerator off coach batteries while driving, after 3-4 hours on the road the low voltage alarm goes off. Plugging in to a campground 30 amp 110V charges the coach batteries nicely.
So, the engine alternator is not charging the coach batteries: either the charging/auxilary-start solenoid is bad - and I plan to replace this original 2002 part in any event, the charging circuit from engine to coach batteries is fauty - and I'm asking VW service to test this, or something in the circuitry of the refrigerator is misbehaving and pulling more amps than the alternator can keep up with. I'll look at the Aux switch next.
NB: the batteries are less than a year old, marine deep-cycle heavies.
Bill Blask, South Carolina