My relay in the battery box has an internal diode it seems.  Disconnects the
fridge from the main battery when the motor isn't running.  I used it to
disconnect the main from the auxiliary battery when the motor isn't running
thereby allowing the auxiliary battery to run the accessories including the
DC fridge without affecting the capacity of the main.  When the motor is
running the aux charges from the alternator.

Clever, those chermans.

pensioner