Free tool
12V fridge overnight draw
Turn a fridge's average amp draw into amp-hours for a night, and compare that with the battery you actually have.
How overnight draw is built
A compressor does not pull its rated amps every minute. The useful number for a night is an average. Dometic prints one for the CFX3 45: 1.03 amp-hours per hour in a 32°C room with the inside at 4°C and Bluetooth on. Engel’s fact sheet for the MT45 prints a range, 0.7 to 2.5 amps, which is not the same kind of number. The presets are labeled that way so you do not treat a range as a lab average.
Ten hours is the default window because that is a long parking break, not because your truck sits for ten hours. Change it. If the socket dies with the key, the fridge is off no matter what this page says, and the amp-hour total is a plan for a socket that stays live.
A 24 volt selection halves the 12 volt current on the assumption that the fridge uses the same power. Confirm that in the manual before you trust it on a 24 volt truck. Other loads are not added. A coffee maker on the same fuse is a separate problem.
To put the fridge next to a CPAP, a fan, and a laptop, use the Sleeper Cab Power Planner. Related: fridge guide.