12V fridge battery calculator

A fridge is usually the biggest power user in a rig, and it runs day and night. Enter what your fridge uses and how many days you want to go without driving or plugging in, and this tells you the battery size to aim for.

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Use the maker's hot-weather figure. A fridge works much harder on a hot day, so take its power use for the hottest weather you'll camp in, from its manual or spec sheet. Anything running on 230V or 120V mains power, such as a shore-power charger or inverter outlet wired into the rig, needs a licensed electrician.

How the sum works

  1. Daily use. Amp-hours per day. Amp-hours per hour × 24, or average watts × 24 ÷ 12 volts.
  2. Days off the grid. Daily use × the number of days.
  3. Usable capacity. You can't run a battery flat. The calculator counts on using about 80% of a lithium battery and 50% of a lead-acid one, then divides by that share.
  4. Solar (optional). Daily use × 12 volts ÷ your sun hours, plus about 15% for losses.

The fridge is only part of it. Add your lights, fans and phone charging to the daily figure if they run off the same battery.

Sources