How Much Power Does a 12V Fridge Use Overnight?
A single zone Dometic CFX5 fridge uses about 10 to 13 amp hours over a 10 to 12 hour night on a 90°F day, based on Dometic's own 12V energy figures. Mild nights use less. A big dual zone fridge running a freezer side can use 28 to 33 amp hours.
This guide shows where those numbers come from, how to size a battery for them, and the habits that cut overnight draw. Every figure is Dometic's published number or simple math on it. Where Dometic does not publish a number, we say so.
The short answer
- Single zone, 25 to 45 liters: about 1.0 to 1.1 amp hours per hour at 12V on a 90°F day with the fridge set to 39°F. That is roughly 10 to 13 Ah per night, or about 125 to 160 watt hours.
- With an ice maker running: the CFX5 55IM is rated at 1.55 Ah per hour with its ice maker in maintenance mode, about 16 to 19 Ah per night.
- Dual zone with a freezer side: the CFX5 75DZ is rated at 2.76 Ah per hour with one zone at 39°F and the other at 5°F, about 28 to 33 Ah per night.
- Power setup: a starter battery is fine for a short stop with the fridge on its HIGH battery protection setting. For overnight use, Dometic recommends a house battery.
Overnight power use by fridge
| Fridge | Size | Avg Ah per hour | 10 hr night, Ah | 12 hr night, Ah | 12 hr night, Wh | Price |
|---|---|---|---|---|---|---|
| CFX5 25 | 25 L | 1.03 | 10.3 | 12.4 | 148 | $899.99 |
| CFX5 35 | 36 L | 1.11 | 11.1 | 13.3 | 160 | $999.99 |
| CFX5 45 | 46 L | 1.05 | 10.5 | 12.6 | 151 | $1,049.99 |
| CFX5 55IM | 55 L | 1.55* | 15.5 | 18.6 | 223 | $1,199.99 |
| CFX5 75DZ | 75 L | 2.76** | 27.6 | 33.1 | 397 | $1,349.99 |
How to do the overnight math
The formula
Average Ah per hour × hours = amp hours used. Amp hours × 12 = approximate watt hours.
CFX5 35 on a hot 12 hour night: 1.11 × 12 = 13.3 Ah, or about 160 Wh.
Use the average figure, not the rated current. Dometic explains that rated current is what the fridge pulls while the compressor is running, and energy consumption is the average amp hours it uses on 12V for a given outside and inside temperature. The compressor cycles on and off, so a CFX5 35 rated at 7.6 A averages about 1.1 A over an hour in Dometic's 90°F rating. Use the rated current only for wiring and fuse sizing.
Hot night vs mild night
Dometic publishes its 12V energy figures at one condition: 90°F outside. It does not publish a figure for a cooler night, so we will not put a number on it. What Dometic does say is that energy use depends on the outside temperature and the temperature you set inside. On a 60°F night the compressor has less heat to pull out, so it runs less and the night total comes in under the table. Plan your battery on the 90°F number and treat mild nights as extra margin.
Afternoon heat carries into the night too. A fridge parked in the sun all afternoon, or one that just got loaded with warm drinks, runs longer into the evening while it catches up.
What power setup you need
Starter battery only. Fine for driving days and short stops. Set the fridge's battery protection to HIGH, which Dometic recommends for a starter battery, so it shuts off while there is still charge left to start the engine. Dometic's manual says that if the engine will be off for a long time, switch the fridge off or run it from a house battery.
House battery. A second battery, isolated from the starter battery, is what Dometic recommends for overnight use. Set the fridge's battery protection to LOW on a house battery so you can use more of it. Our guide on how to set up a dual battery system for overlanding covers isolators, DC to DC chargers and battery types.
Portable power station. Check its usable watt hours against the table. For two nights without charging, double the night total, and keep a margin for hot afternoons and lid openings.
Wiring. If the fridge shows a low voltage alert on a charged battery, Dometic's manual points to voltage drop in the wiring and says to increase the wire gauge.
How to use less power overnight
- Pre-chill at home. Run the fridge on AC power the day before so the battery is not pulling it down from warm.
- Pre-cool the food and drinks. Dometic advises letting warm food cool before it goes in. Load cold cans from the house fridge, not the pantry.
- Leave a ventilation gap. Dometic calls for at least 2 inches (50 mm) of space on all sides of a CFX5.
- Keep it in the shade. Dometic says to keep the fridge out of direct sunlight.
- Open the lid less. Decide what you want before you open it, and close it fully. Check the lid seal if the fridge runs more than it used to.
- Do not set it colder than you need. Dometic lists unnecessarily low temperatures as a source of extra draw. The CFX5 manual does not describe an eco mode, so the set temperature is your main lever.
- Turn off what you are not using. Switch off the ice maker on the 55IM when you have enough ice, and switch off the second zone on the 75DZ if you do not need it.
- Set battery protection to match the battery. HIGH on a starter battery, LOW on a house battery.
Fridges and wiring for overnight power
Dometic CFX5 55IM: $1,199.99
The 55IM adds an ice maker. Dometic rates it at 1.55 Ah per hour at 90°F with the ice maker in maintenance mode, about 18.6 Ah on a 12 hour night. The manual says the ice maker makes ice fast for a few hours, then drops into maintenance mode to save energy, and that it ships switched off.
Why pick it
- Ice at camp without buying bags
- 55 liters for longer trips or bigger groups
- Ice maker can be switched off when you have enough
Trade-offs
- Higher overnight draw than the single zone models with the ice maker on
- Dometic does not publish a figure with the ice maker off
Dometic CFX5 75DZ: $1,349.99
Two zones, 75 liters. Dometic rates it at 2.76 Ah per hour at 90°F with one side at 39°F and the other at 5°F, about 33 Ah on a 12 hour night. That draw comes from running a true freezer side, so size the battery for it before you buy.
Why pick it
- Fridge and freezer in one unit
- Either zone can be switched off
- Largest capacity in the CFX5 line we carry
Trade-offs
- About 2.5 times the overnight draw of the CFX5 35 in Dometic's rating
- Needs a house battery for overnight use
- Dometic does not publish a single zone figure
Dometic HWK-DC hardwiring kit: $54.99
The HWK-DC runs 20 feet of 10AWG cable with a 15A blade fuse from your starter or auxiliary battery to a surface or panel mount housing. It has a standard DC socket and Dometic's 2 pin threaded socket, which locks the CFX5 plug in place. It works on 12V and 24V.
Why pick it
- Heavy gauge wire to cut voltage drop at the back of the vehicle
- Threaded socket keeps the plug from working loose on rough roads
- Works with CFX coolers on 12V or 24V
Trade-offs
- You run the cable and mount the housing yourself
- Does not add battery capacity on its own
Questions about 12V fridge power
How many amp hours does a single zone Dometic CFX5 use overnight?
About 10 to 13 amp hours over a 10 to 12 hour night. Dometic rates the single zone CFX5 models at 1.03 to 1.11 Ah per hour on 12V with 90°F outside and 39°F inside, so a 12 hour night works out to about 12.4 to 13.3 Ah. A mild night uses less.
Why is the rated current 7.6 A if the fridge averages about 1.1 amp hours per hour?
Rated current is what the fridge pulls while the compressor is running. The compressor cycles on and off, so the average over an hour is much lower. Use the average for battery sizing and the rated current for wiring and fuses.
Can I run a CFX5 off my starter battery overnight?
Dometic recommends against it. Its manual says to set battery protection to HIGH on a starter battery and, if the engine will be off for a long time, to switch the fridge off or run it from a house battery.
Does the ice maker on the CFX5 55IM use more power?
Yes. The manual says energy use goes up with the ice maker on and suggests switching it off when you do not need ice. After a few hours of fast ice making it drops into a maintenance mode that uses less. Dometic rates the Dometic CFX5 55IM at 1.55 Ah per hour with the ice maker in that mode.
Why does my fridge show a low voltage alert when the battery is charged?
Dometic's manual points to voltage drop between the battery and the outlet and says to increase the wiring gauge. The Dometic HWK-DC hardwiring kit uses 10AWG cable for that reason. A battery protection setting that is too high for your battery can also trigger it.
Sources
Specs checked on Dometic's US site and in the CFX5 operating manual on October 31, 2026.
- Dometic CFX5 25 specifications
- Dometic CFX5 35 specifications
- Dometic CFX5 45 specifications
- Dometic CFX5 55IM specifications
- Dometic CFX5 75DZ specifications
- Dometic support: rated current vs energy consumption
- Dometic CFX5 operating manual (PDF)
- Dometic Hardwiring Kit DC specifications
Ready to size your setup? For overnight power planning, compare the Dometic CFX5 55IM with its ice maker and the dual zone Dometic CFX5 75DZ in the table above, and add the Dometic HWK-DC hardwiring kit to get clean power to the back of your rig.