I finally gave up on my NOcold 1200 and installed a 21 cuft home refer. I added a separate battery bank (500 AH AGM) and a 1000W PSW inverter with a 100 amp charger and transfer switch as we boondock often. When running it's 8 amps into the inverter (100W) and 22 amps during the icemaker harvests cycle. Amazing how energy efficient these Energy Star refers have gotten. The compressor is not much bigger than a grapefruit. Just got back from first camping trip with it and I did a test of my battery system even though we had power. Did not get on the DW about leaving the door open too long...:B and used a fair amount of ice. The batteries started at 13.2V and 24 hours later they were at 12.5V. After one hour with the 100 amp charger they were back to 13.2V. Could probably go 36 hours before reaching the 50% point on the batteries but we usually run the generator every evening.
OP, while one battery might go 12 hours, you really need two for it and two for the 5er... total of four.