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Cab Tools

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.

12V Fridge Battery Runtime Estimator

Fridge type

Follows the fridge type above, but stays editable. Compressor fridges cycle — this is the average draw, not the running watts on the label. Example: a Dometic CFX3 45 draws about 45 W while running on DC (Dometic spec).

Total amp-hours of the bank feeding the fridge. A pair of Group 31 truck batteries is roughly 200 Ah.

Battery chemistry

Follows the chemistry above, but stays editable. Draining lead-acid past ~50% shortens its life — lithium handles deep discharge far better.

Estimated runtime
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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.