Short answer: a 12V compressor fridge pulls about 4 to 5 amps while the compressor is actually running, but that’s not the number you should size your battery on. Averaged across a full day – because the compressor switches off once it hits temperature – a typical mid-size fridge works out to roughly 1 amp-hour per hour, or somewhere around 25 to 40 amp-hours over 24 hours. That’s the figure that decides everything.
The confusion that wrecks people’s power planning is treating the compressor’s running draw as if it ran all day. It doesn’t. Here’s the difference between peak draw and average draw, the real measured numbers from fridges people have actually metered, what pushes the figure up, and how to turn it into a battery or power station size.
The two numbers people mix up: peak draw vs duty cycle
A compressor fridge has two draws that matter. Running draw is what it pulls while the compressor is on – about 45 to 60W, which at 12V is roughly 3.5 to 5 amps. Average draw is what it pulls over time, and that depends on the duty cycle: the fraction of the hour the compressor actually runs. In mild weather a well-insulated fridge cycles maybe a third of the time. So 5 amps for 20 minutes an hour is about 1.7 amp-hours that hour, not 5.
Real measured numbers (not nameplate maximums)
These are figures from independent testers who metered the fridges over many hours at fridge temperatures (around 38°F) in moderate ambient – the conditions you’ll actually camp in. Notice how close the good brands land, and how much the running-amps figure overstates real consumption.
| Fridge (size) | Avg draw | Over 24 hours | Tested by |
|---|---|---|---|
| Dometic CFX3 45 (~47L) | ~0.87 Ah/hr | ~21 Ah | Trail4Runner bench test |
| Dometic CFX3 55IM (~53L) | ~1.03 Ah/hr | ~24.8 Ah | Trail4Runner bench test |
| Dometic CFX3 75DZ (~75L) | ~1.29 Ah/hr | ~31.1 Ah | Trail4Runner bench test |
| Iceco VL60 (60L) | ~1.0-1.1 Ah/hr | ~24-26 Ah | CampAddict / owner reports |
| Iceco VL35 ProS (35L, in heat) | ~1.76 Ah/hr | ~42 Ah (~508 Wh) | GNOMAD Home real-world |
Two things jump out. First, a bigger fridge doesn’t draw proportionally more – insulation and compressor efficiency matter more than raw litres. Second, that Iceco VL35 number is higher than the bigger Dometics, because it was tested in warmer conditions and is a punchier “Pro” unit. Heat, not size, is the biggest lever. Treat ~1 Ah/hr as the mild-weather baseline and assume it climbs from there.
Those amps still have to get to the fridge. On a long run of thin wire part of the voltage never arrives, and the fridge shuts off with a healthy battery. What gauge wire for a 12V fridge has the numbers by length.
What pushes the number up (sometimes a lot)
- Ambient heat. The single biggest factor. A fridge in a hot car or full sun can draw 50% more than the same fridge in the shade. Testers and manufacturers agree on this. Park in shade, throw a cover on it, and give the vents air.
- Freezer vs fridge temperature. Running it as a freezer (0°F) instead of a fridge (38°F) roughly doubles the work. Dual-zone freezing on one side costs you.
- Opening the lid. Every time you open it, cold air falls out and the compressor has to recover. Frequent rummaging in hot weather adds up.
- Poor ventilation. Boxed-in compressors can’t shed heat and run longer. Leave a gap around the condenser end.
- Low battery voltage. As the supply sags, the fridge draws more current for the same power. Another reason lithium (which holds voltage) beats a tired lead-acid battery here.
- Warm food and drinks. Pulling a full load of warm cans down to temperature is a big one-off hit. Pre-chill at home if you can.
Most decent fridges have an ECO mode that softens the compressor and can cut consumption meaningfully – some makers claim up to half – at the cost of slower cooling. Off-grid, leave it in ECO unless you’re pulling a warm load down.
Turning amp-hours into a battery (the useful part)
Now the number earns its keep. Say your fridge averages 30 Ah a day. A 100Ah lithium (LiFePO4) battery gives you most of its capacity usefully, so it runs that fridge for roughly three days with nothing else drawing on it. A 100Ah lead-acid or AGM battery you should only pull down halfway, so call it ~50 usable Ah – more like a day and a half. Same sticker, half the real runtime. That gap is why everyone’s switched to lithium.
And if the battery in question is the one that starts the car, those same amp-hours answer a different question: can you run a 12V fridge off your car battery overnight?
Prefer to think in watt-hours and power stations? Multiply Ah by 12: 30 Ah a day is about 360Wh a day. We do that full conversion, including running off the DC output to save the inverter loss, in how long a power station runs a 12V fridge, and the whole-setup sizing in what size power station you actually need.
Wiring a battery into the vehicle instead of carrying a power station? That amp-hour figure is the first of the five numbers in the dual-battery setup guide for overlanding, which goes on to size the house battery, the DC-DC charger and the cable.
Amp-hours tell you how long the battery lasts. The fridge’s low-voltage cutoff decides when it stops trying, and High is not the same voltage on every brand. 12V fridge low-voltage cutoff explained has the table.
The mistakes that wreck the estimate
- Sizing off the running watts. “It’s 60W, that’s 5 amps, 120 amp-hours a day!” No – it only runs part of the time. That mistake makes people buy double the battery.
- Ignoring heat. The mild-weather number is a floor, not a promise. Plan for a hot day or you’ll be flat by morning.
- Trusting 100Ah of lead-acid as 100Ah. You get about half usefully before you damage the battery. Lithium is the honest 100Ah.
- Thermoelectric “coolers.” The cheap iceless coolers draw a constant 4-5 amps all day with no duty cycle and can’t get truly cold. Different beast, far worse for off-grid. A real compressor fridge uses less power and actually keeps food safe.
Related: how long a power station runs a 12V fridge · best 12V fridge for overlanding · what size power station you need · best power stations for car camping.
The receipts: what I read and watched
- Hard numbersCFX3 Power Consumption Test (metered Ah over 24-48h) ↗ – Trail4RunnerMeasured the Dometic CFX3 45/55IM/75DZ at ~0.87-1.29 Ah/hr – the per-model figures in the table.
- Expert reviewIceco VL35 ProS real-world power draw ↗ – GNOMAD HomeLogged ~1.76 Ah/hr / ~508Wh over 24h in warm conditions – shows how much heat lifts the number.
- Expert reviewIceco VL60 review and consumption ↗ – CampAddictOwner-level draw around 1 amp/hr at fridge temps, with ECO mode reducing it.
- Hard numbersHow Much Power Does a 12V Camping Fridge Use ↗ – National LunaExplains duty cycle and why ambient heat is the dominant variable.
- Owner reports12V fridge recommendations + real consumption ↗ – r/overlanding via Overland BoundOwners repeatedly land near ~30 Ah/day and warn against sizing off running watts.
FAQ
How many amps does a 12V fridge draw per hour?
While the compressor runs, about 4-5 amps. Averaged over an hour (the compressor cycling on and off), about 1 amp-hour for a mid-size fridge in mild weather – rising toward 1.5-2 Ah/hr in heat or for thirsty “Pro” units.
How many amp-hours does a 12V fridge use per day?
Roughly 25 to 40 amp-hours over 24 hours for a typical 35-60L fridge at fridge temperature in moderate conditions. Metered tests put the Dometic CFX3 range at ~21-31 Ah/day. Heat, freezing, and frequent opening push it higher.
How long will a 100Ah battery run a 12V fridge?
A 100Ah lithium (LiFePO4) battery runs a ~30 Ah/day fridge for about three days on its own. A 100Ah lead-acid or AGM only gives ~50 usable Ah, so more like a day and a half. Lithium holds voltage and tolerates deep discharge, which is why it lasts roughly twice as long from the same sticker rating.
Does a bigger fridge always use more power?
Not proportionally. Insulation quality, compressor efficiency and ambient heat matter more than raw litres – a well-built 75L fridge can draw barely more than a cheap 35L one. Build quality beats size for efficiency.
Is ECO mode worth using?
Off-grid, yes. ECO eases the compressor and can cut consumption noticeably (some makers claim up to half), trading slower cooling for longer battery life. Leave it on unless you’re pulling a warm load down to temperature quickly.
