Battery runtime
How Long Will a 100Ah Battery Run a Fridge?
A 100Ah battery can run a camping fridge anywhere from about one day to several days depending on the fridge, battery chemistry, temperature, insulation, and whether solar or alternator charging is replacing energy.
The basic math
Most overlanders buy batteries in amp-hours, but most appliances are easier to understand in watts. Convert the battery to watt-hours first.
Battery Wh = Amp-hours x VoltageFor a 100Ah LiFePO4 battery with a nominal voltage around 12.8V:
100Ah x 12.8V = 1,280WhIf your fridge averaged 40W over time, the simple estimate would be:
1,280Wh / 40W = 32 hoursExample fridge runtimes
| Average draw | Estimated runtime | Best use case |
|---|---|---|
| 30W | 42.7 hours | Efficient fridge, mild weather, good airflow |
| 40W | 32 hours | Typical overland fridge planning number |
| 50W | 25.6 hours | Hot weather, larger fridge, frequent opening |
Why real-world runtime changes
A compressor fridge does not usually pull its full rated wattage all day. It cycles on and off. The duty cycle depends on ambient temperature, how cold you set it, how often you open it, how much food is inside, and whether the fridge can vent heat.
Hot desert camping, direct sun, poor airflow, and warm food loaded into the fridge can all increase power use. Pre-chilling the fridge at home, parking in shade, and keeping it full can reduce cycling.
Battery chemistry matters
LiFePO4 batteries usually allow much deeper usable capacity than AGM or flooded lead-acid batteries. A 100Ah lithium battery may provide around 90% usable capacity, while lead-acid systems are often planned around 50% usable capacity to preserve battery life.
That means two 100Ah batteries with the same label can behave very differently on trail.
Can solar keep the fridge running?
Solar does not make the fridge free. It replaces energy removed from the battery. If a fridge uses 500Wh per day and a 100W panel produces around 400-500Wh on a good day, solar may keep up in clear weather. Shade, clouds, panel angle, roof rack shadows, and dust can reduce output fast.
Fast recommendation
For a weekend fridge-only setup, a 100Ah LiFePO4 battery is often a strong starting point. For hot climates, long stationary camps, Starlink, heated blankets, laptops, or poor solar conditions, 200Ah gives much more breathing room.
Use the Overland Watts runtime calculator to estimate your own fridge and battery setup.