Today I went to retreive coach and make ready for trip. Started fine and runs fine, but before leaving for home (118 miles away) I noticed alternator was not charging. Read 10v and then dropped steadily to 8v. Shut it down. Tried the Aux switch to restart but no joy. It has a new smart charger on it and the house batteries are fine. Plugged back into shore power and coach started. So removed the alternator and drove to Houston (no local repair services in College Station of Bryan Texas) and the technician tested the alternator and declared it good. Told me the chassis batteries have to be close to 12v or the regulator will not function and will not connect the alternator to the load. Says if I charge the batteries all should be well. Questions: Does a properly connected smart charger keep both coach and chassis batteries charged? Why does the Aux switch not connect (or maybe it did but the chassis batteries were too low) so I can start the coach? I thought it was supposed to paralle all the batteries. Is there a series of relays or fuses that need to be checked? If so can anyone suggest where they might be? BTW this is a CAT 3208T in a 1993 Regency with a Gillig Chassis. Thanks in advance.

The typical converter charges only the house batteries (because the coach is wired that way).

The alternator charges both house and chassis batteries through the isolator (which may be a relay rather than solid-state).

Something is odd, in that you were able to start but then the voltage started dropping. Possibly a fusible link has blown. I'd start by checking alternator output at the chassis battery then work backwards.

However, before doing that, I'd check chassis grounds, especially the primaries for the batteries.