How long will a 12V fridge run on a car battery? Hours for every Dometic CFX
Hours on a car, AGM or lithium battery for each current Dometic CFX3 and CFX5 12V fridge, from Dometic's own average consumption figures at 90 F.
Average consumption from Dometic's product pages, read by hand. We have not measured these fridges ourselves. How we research | How links work
The short answer
About 95 hours on a 100 Ah lithium (LiFePO4) battery for a Dometic CFX5 45, and about 48 hours on a 100 Ah lead-acid or AGM battery, which Dometic counts as only 50% usable. That uses Dometic's own average of 1.05 Ah per hour on a hot day (32 C outside, 4 C inside). The 9 CFX models below range from 0.92 to 2.76 Ah per hour. A starter battery is the risky case: keep the fridge's battery protection on High or Medium, as Dometic advises, so the car still starts.
Hours on your battery
About 95 hours
On a hot day, from Dometic's average figure. Cooler weather gives more.
Hours for each Dometic CFX fridge
Dometic's stated average 12 V consumption for each model, and the hours that gives on two common batteries: a 100 Ah lead-acid or AGM battery (50 Ah usable) and a 100 Ah LiFePO4 battery (100 Ah usable). Sorted by size.
| Fridge | Litres | Zones | Average draw (Ah per hour) | Hours on 100 Ah lead-acid | Hours on 100 Ah LiFePO4 | Rated maximum at 12 V | Source |
|---|---|---|---|---|---|---|---|
| Dometic CFX3 25 | 25 | Single | 0.92 | 54 | 109 | 6.5 A | Dometic |
| Dometic CFX5 25 | 25 | Single | 1.03 | 49 | 97 | 7.2 A | Dometic |
| Dometic CFX5 35 | 36 | Single | 1.11 | 45 | 90 | 7.6 A | Dometic |
| Dometic CFX3 45 | 46 | Single | 1.03 | 49 | 97 | 8.2 A | Dometic |
| Dometic CFX5 45 | 46 | Single | 1.05 | 48 | 95 | 8.1 A | Dometic |
| Dometic CFX3 55IM | 53 | Single, ice maker | 1.11 (1.20) | 45 | 90 | 8.9 A | Dometic |
| Dometic CFX5 55IM | 55 | Single, ice maker | 1.55 | 32 | 65 | 8.5 A | Dometic |
| Dometic CFX5 75DZ | 75 | Dual zone | 2.76 | 18 | 36 | 9.7 A | Dometic |
| Dometic CFX5 95DZ | 94 | Dual zone | 1.53 (3.26) | 33 | 65 | 9.8 A | Dometic |
Figures in brackets are Dometic's second test: the CFX5 95DZ with its small zone at -15 C as a freezer, and the CFX3 55IM with its ice maker on. The CFX5 75DZ figure is with its small zone as a freezer, which is why it is the highest. The CFX5 models use R1234yf refrigerant, the CFX3 models R134a. The CFX3 45 and CFX3 55IM figures come from Dometic's international page for the same item number, because the US page did not load when we checked.
On the starter battery
The table assumes a battery you can use down to its usable share. A starter battery is there to start the engine, so the question is not how many hours but when the fridge should stop. Dometic's CFX fridges have a 3-stage battery protection that measures the voltage while the compressor runs and turns the fridge off below the chosen level. Dometic recommends High or Medium on a starter battery and Low only on an accessory or dual battery.
Dometic also points out that the voltage drops under load, so a battery that reads 12.8 V at rest can trip the protection when the compressor starts. Dometic advises against splitters, pigtails and extension leads, because each adds voltage loss along the cable. If the fridge still will not turn on with a recommended setting, Dometic suggests trying one level lower.
Next step
Find your fridge's average Ah per hour on its spec sheet, check your battery's Ah and type on its label, and divide. For more than one night away from a charger, plan on an accessory battery rather than the starter battery.
Common questions
Can I run a 12V fridge overnight on my car battery?
Dometic built its 3-stage battery protection for exactly this case: it monitors the voltage and switches the cooler off to stop it draining the starter battery. Dometic recommends the High or Medium setting on a starter battery and Low only on an accessory or dual battery. For several nights, use a separate battery.
Why is the rated current so much higher than the average?
The rated input current is the most the fridge can draw, for example 8.1 A for the CFX5 45. Dometic says to use it for sizing wires. The compressor cycles on and off, so the average over an hour is far lower: 1.05 Ah on Dometic's hot-day test.
Do other brands publish a comparable figure?
Not on the product pages we read on 17 October 2026, so they are not in the table. Rated watts or amps are a maximum, and dividing a battery by them would understate the hours: on the Dometic models above, the rated current is 3 to 8 times the average.
Will it run longer in cool weather?
Yes. Every figure here comes from a 32 C (90 F) outside temperature with the inside at 4 C (39 F), so it is a hot-day number. Dometic also notes that even small changes to the set temperature change the consumption.
Method
- Consumption. Dometic's "Energy Consumption 12VDC" figure in Ah per hour, read by hand from each product page on 17 October 2026, at the test condition Dometic states (32 C or 90 F outside, 4 C or 39 F inside).
- Usable battery. Dometic's own guidance: lead-acid about 50% of the stated Ah, lithium NMC about 80%, LiFePO4 nearly 100%. We use 100% for LiFePO4.
- Hours. Usable Ah divided by Ah per hour, the method Dometic gives on its product pages.
- Not covered. We did not measure any fridge. Door openings, warm food, sun on the cooler and cable losses all raise the draw. Brands that do not publish an average consumption figure are left out rather than estimated.
Sources
- Dometic product pages for each fridge (electrical and performance specifications), linked in the table, read 2026-10-17
- Dometic CFX3 45 page, FAQ: average consumption vs rated current, usable share by battery chemistry, 3-stage battery protection, read 2026-10-17
- Our Dometic 12V fridge consumption dataset, CSV
Changes
- : Published. 9 Dometic CFX3 and CFX5 models, each read on Dometic's product page on 17 October 2026.