Power & water
Intermediate
· 1 min read
Work out a power budget for your 12 V fridge
How long a battery will really run your fridge, and the simple maths to check it.
A compressor fridge doesn't run all the time; it cycles. What matters is how much energy it uses over a full day.
The quick estimate
Most 40–50 L compressor fridges use roughly 15–30 amp-hours a day at 12 V in mild weather. That's about 180–360 watt-hours. In hot weather, or if the lid opens often, plan for more.
To estimate run time:
usable battery watt-hours ÷ daily fridge use = days
A 1000 Wh lithium battery with about 90% usable is roughly 900 Wh. At 300 Wh a day, that's about three days before you need to recharge.
Make it last longer
- Pre-cool the fridge and the food at home on mains power.
- Keep the fridge in the shade with space around the vents.
- Use an insulated cover.
- Open the lid less. Pack drinks in a separate esky.
- Add solar: a 200 W panel in good sun can replace most of a day's fridge use.
Check your fridge's manual for its actual consumption. Manufacturers publish it, and it's the number your budget should use.