Thor Forums

[Chance]

The battery 27 group size is likely 80 Amp-hours per battery at 12 Volts and not 160 Amp-hours each (as assumed by GMC). If it were a 6-Volt battery it could easily be rated at 160 Amp-hours each, but since the two would end up in series instead of parallel (as done with 12-Volt batteries) then we'd still be at 160 Amp-hours total at 12 Volts.

Assuming batteries are in great shape, and state of discharge is limited to 50% for design purposes, then we'd expect 80 Amp-hours of usable capacity.

If a fridge draws 1 Amp on average (and that's at 120 Volts AC), then the inverter will need a little over 10 Amps of 12-Volt DC juice from batteries. And if battery energy is limited to 80 Amp-hours, then fridge may run up to 8 hours provided nothing else is operating (and also that batteries start at 100% of rated capacity).

One can quickly see why residential refrigerators often come with 4 fairly large quality batteries. Combined with the fact that the refrigerator normally doesn't operate 100% of time, and that batteries can go below 50% state-of-charge, it's easy to predict up to 1 to 2 days of operation.

Obviously a more efficient refrigerator will run longer on same batteries. A more efficient inverter helps a little too, as well as when refrigerator is in cool camper versus one in hot camper. There's a lot to consider when estimating run time.