As "1987_345" described his situation,it is exactly the same issue I've been having. To clarify a couple of things, it is the engine battery that discharges, not the coach batteries that discharge. This happens with engine running and generator running at the same time. Honestly I have not yet checked to see I'd the engine batt gets charged by the genset with engine not running. Also, the transfer switch transfers power solely based on sensing 120 volts from shore or genset. There is no 12 volts wired to the switch.