Updated September 2026
12V Power
12V fridge battery runtime estimator
Fridge watts in, battery amp-hours in — see how many hours of cold you actually have before the bank is flat. Still shopping? Compare the winners in our best 12V coolers for truck drivers ranking.
Illustration, not a product photo.
How long will the fridge run before the battery is flat?
Fridge draw and discharge figures are typical published values — your fridge manual and battery spec sheet are the source of truth. Every input stays editable.
Won’t last a full rest period. Either grow the bank, add solar to top it up by day, or run the fridge colder while driving and let it coast overnight.
That is a big average draw. Above ~80 W average you are likely looking at freezer mode in serious heat — pre-cool on shore or engine power before you park.
- Compressor fridges cycle on a thermostat — average draw is what matters here, not the running watts on the label.
- Usable percentages are planning figures, not lab measurements — old or cold batteries deliver less.
- This estimates fridge runtime only. Lights, fans and inverters draw from the same bank.
- Keep the truck-start reserve in mind: never plan to use the cranking batteries to zero.
Ah × 12 V × DoD % ÷ fridge W = hours
Steady average draw. Thermostat cycling and cool nights usually stretch real runtime past this number.
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Research-based. We did not test these hands-on. Draw figures are typical published specs (e.g. Dometic CFX3 45: ~45 W DC running per Dometic’s spec) — your fridge manual is the source of truth. Depth-of-discharge percentages are planning figures, not battery-lab measurements. Change any input and the math re-runs.