How Long Will a 12V Fridge Run on a 100Ah Battery?

Short answer: 2 to 4 days for a typical 12V compressor fridge, assuming you’re using a LiFePO4 battery and conditions aren’t extreme.

That’s a wide range, and here’s why: fridges don’t draw constant power. They cycle on and off throughout the day, and how often they run depends mostly on one thing — how hot it is outside.

The Real Power Draw of a 12V Fridge

A typical 40-50L camping fridge draws 30-60 watts while the compressor is running. But the compressor doesn’t run continuously — it kicks in when the temperature rises, cools things down, then shuts off.

This cycling behavior is called duty cycle, and it’s usually somewhere between 25% and 50% depending on conditions:

• Cool weather, fridge in shade: compressor runs ~25% of the time
• Hot day, fridge in direct sun: compressor runs 40-50% of the time

In practice, most 12V compressor fridges consume 250-500 Wh per day (roughly 20-40 Ah from a 12V battery). That’s the number that actually matters for planning.

Runtime Estimates

For a 12.8V 100Ah LiFePO4 battery (~1,150 Wh usable):

If you’re using a lead-acid or AGM battery, cut these numbers roughly in half — you can only safely use about 50% of the capacity.

What Affects Runtime Most?

Ambient temperature is the biggest factor. The hotter it gets around your fridge, the harder it works. Testing shows that going from 70°F to 110°F (21°C to 43°C) can triple how often the compressor runs.

Other factors that matter:

• How often you open the door — every time warm air rushes in, the compressor has to work harder
• Pre-cooling — a fridge that’s already cold uses less energy to maintain temperature
• Fridge placement — shade vs. direct sun makes a huge difference
• Insulation quality — better insulated fridges cycle less often

One thing that doesn’t matter much: how full the fridge is. A full fridge actually holds temperature better because the thermal mass helps stabilize things.

Calculate Your Setup

For fridge runtime, enter the average power draw — not the compressor’s running wattage. A good starting point is 30-40W for a medium camping fridge in moderate conditions.

Tips for Longer Runtime

Pre-cool at home before you leave. Starting with a cold fridge saves significant battery during the first few hours.

Keep it in the shade. This alone can cut energy use by 20-30%.

Use an insulated cover if your fridge came with one (or buy one). They’re not just marketing — they actually help.

Minimize door openings. Pack strategically so you’re not digging around every time you want a drink.

Consider a dual-battery setup. If you’re running the fridge from your vehicle, a secondary battery protects your starter battery from getting drained.

Keep It Cool, Enjoy the Moment

Once your setup is dialed in, you can stop worrying about the numbers. Whether you’re parked by a lake, deep in the mountains, or just escaping to your favorite quiet spot, there’s nothing quite like reaching into your fridge and pulling out an ice-cold drink. That first sip hits different when you’re surrounded by nature, off the grid, and completely free. Here’s to cold beers, fresh food, and adventures that don’t come with a power cord.

Ready to plan your setup? Use the calculator above with your specific fridge and battery, or check out:

How Long Will a 100Ah Battery Last? — more runtime scenarios and examples

Last updated: December 2025