3 Batteries, 2 banks, one boat
Rod,I did what you are trying to do. Two batteries (A & B) wired together to make 12 volts make my first (primary house) bank. One battery (C) solo is my second (primary starting) bank. But (C) is still a deep cycle. Either bank can start motor or run fridge. Two things I did that I think help. First, the charger has three charge post but was orginal setup for two batteries in total. So there was a "jumper wire" combining +2 and +3. (these wires were also run through the selector switch. I ran the wires (#1, 2,& 3) direct from charger to each respective battery. So while on shore power, everybody (A, B, & C) gets juiced! When motoring, I "generally" put selector on "Both" so all batteries get some current. Just remember to switch to your house bank when the motor is off.Second thing, put in a block of ice and turn off the fridge while sailing or at anchor. Along the same lines, we put water bottle in the freezer are while at the dock and as they freeze we move them to the fridge. Unless you're gone for over three days, you can make it.(one last suggestion-pre freeze all the cold items you can.