[C320-list] Protecting The Batteries when away from boat at dock

[Ken Geiger]

In the Flooded Battery Thread, Warren mentioned a devise to sense low battery and then disconnect the load (the reefer).
  I quote;

"For those who leave refer running while away from boat, there is a device
that will sense State of Charge and disconnect a load (refer.) This avoids
running a good battery into the ground (below 11 V) should shore power be
lost (a sure way to shorten your battery's life.) Jeff Hare can say more
about this device."

I wonder if one could protect the batteries while leaving the reefer on when at dock and away, by paralleling in a 
110 V relay coil with the parallel 12 V to the reefer on a set of contacts.   The coil would drop out and open the 
power supply to the reefer upon AC power loss thus prevent draining the battery.  

The Reefer switch on the panel would be in the off position and the battery main switch on, supplying the
 parallel 12 V circuit to the reefer through the relay contacts.

Ken Geiger
Northern Dream, 2000 #765