Hi lishka. Our 1992 Fleetwood Colchester 1850 had a Zig unit that required switching from Caravan to Car when being towed.
Likewise if on a CL or anywhere that did not have Hook-up the Zig was left switched to Caravan,then when towing again it would be set to car and be charged up on the return journey.
When we got to site and hooked up it would be first set to caravan after unhooking from the car.
When attached to the site hook-up it automatically charge the battery through the Zig and maintained the voltage.