# How Long Will a Battery Run a 12V Fridge? (Worked Math)

> How long a battery runs a 12V fridge: usable Ah divided by average draw, adjusted for heat.

- Source: https://portablefridgeguide.com/posts/how-long-will-a-battery-run-a-12v-fridge/
- Markdown version: https://portablefridgeguide.com/posts/how-long-will-a-battery-run-a-12v-fridge.md
- Last updated: 2026-10-30

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- How Long Will a Battery Run a 12V Fridge? The Math, With Worked Examples

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# How Long Will a Battery Run a 12V Fridge? The Math, With Worked Examples
  Updated October 30, 2026 By [Portable Fridge Guide Editorial Team](https://portablefridgeguide.com/about/) [How we research](https://portablefridgeguide.com/how-we-research/)

Prices are approximate and change often, so check the current price before you buy.

## Key takeaways

- **Runtime = usable battery Ah ÷ average draw in Ah per hour.** That's the method Dometic publishes for its CFX fridges.
- Count only usable capacity: about 50% of an AGM or lead-acid battery, 80% of lithium NMC, 90% of LiFePO4 and about 85% of a power station's rating.
- Heat matters. Scaled from Dometic's published CFX3 45 figure, a 100 Ah LiFePO4 battery runs a 45-quart fridge for about 5.6 days at 70°F but under 3 days at 100°F.
- Real use can be far hungrier than lab figures. Gnomad Home measured an ICECO VL35 ProS averaging about 1.76 A over 123 hours of camping.
- Put your own fridge and battery into the [battery runtime calculator](https://portablefridgeguide.com/tools/battery-runtime-calculator/).

## Our top picks

- 1![EcoFlow GLACIER Classic 35L](https://portablefridgeguide.com/_astro/ecoflow-glacier-classic-35.BOvSiZZQ_ZK515Y.webp)The only fridge we track with a published fridge-mode draw: 0.57 Ah/h at 77°F[EcoFlow GLACIER Classic 35L](https://portablefridgeguide.com/fridges/ecoflow-glacier-classic-35/)37 qt · Single zone · Down to -4°F · 45 lb7.6**$$$**$PremiumPrice tier: Premium[Check price on Amazon](https://www.amazon.com/dp/B0F62HMKBX?tag=portablefridgeguide.com-20)
- 2![Anker SOLIX EverFrost 2 40L](https://portablefridgeguide.com/_astro/anker-everfrost-2-40.CvK9adOb_27MU9N.webp)Battery in the box: Anker claims up to 52 hours at 39°F in 77°F air[Anker SOLIX EverFrost 2 40L](https://portablefridgeguide.com/fridges/anker-everfrost-2-40/)42 qt · Single zone · Down to -4°F · 50.7 lb8.2**$$$**$PremiumPrice tier: Premium[Check price](https://www.amazon.com/dp/B0DRCNMMZ9?tag=portablefridgeguide.com-20)

### On this page 10 sections

- [What’s the formula?](#whats-the-formula)
- [Why does outside temperature change the answer?](#why-does-outside-temperature-change-the-answer)
- [Worked example 1: a 45-quart fridge on a 100 Ah battery](#worked-example-1-a-45-quart-fridge-on-a-100-ah-battery)
- [Worked example 2: a fridge with its own battery](#worked-example-2-a-fridge-with-its-own-battery)
- [Worked example 3: when real use beats the spec sheet](#worked-example-3-when-real-use-beats-the-spec-sheet)
- [Worked example 4: a power station](#worked-example-4-a-power-station)
- [What about the car’s starter battery?](#what-about-the-cars-starter-battery)
- [How do you get more hours from the same battery?](#how-do-you-get-more-hours-from-the-same-battery)
- [Bottom line](#bottom-line)
- [FAQ](#faq)

## Before you choose

- [How to Power a Portable Fridge: Car Socket, Second Battery, Power Station or Solar](https://portablefridgeguide.com/posts/how-to-power-a-portable-fridge/)
- [Portable Fridge Power Consumption Explained: Watts, Ah/h and Wh per Day](https://portablefridgeguide.com/posts/portable-fridge-power-consumption-explained/)
- [What Size Solar Panel Do You Need for a 12V Fridge?](https://portablefridgeguide.com/posts/solar-panel-size-for-12v-fridge/)

“Will my battery last the weekend?” is the question behind most 12V fridge setups, and the answer is simple arithmetic once you have the right two numbers. This guide shows the method Dometic publishes for its own fridges, the adjustments that matter (battery chemistry and outside temperature), and a set of worked examples. We haven’t measured any of these fridges ourselves. Every figure below comes from a maker’s published spec, an independent review, or our own estimate, and we say which. To skip the math, use the [battery runtime calculator](https://portablefridgeguide.com/tools/battery-runtime-calculator/).

## What’s the formula?

Dometic’s FAQ gives it directly: divide the battery’s usable amp-hours by the fridge’s average consumption in amp-hours per hour (Ah/h). The answer is hours of runtime.

```
runtime (hours) = usable battery Ah ÷ average draw (Ah/h)
```

Two numbers, and both are easy to get wrong.

Usable battery capacity. You can’t drain every battery to zero. Our calculator uses Dometic’s guidance, keeping LiFePO4 at a slightly conservative 90%:

| Battery type | Usable share | 100 Ah battery gives |
| --- | --- | --- |
| Lead-acid / AGM | 50% | 50 Ah |
| Lithium NMC | 80% | 80 Ah |
| LiFePO4 (lithium iron phosphate) | 90% | 90 Ah |
| Power station (rated in Wh) | about 85% | take 85% of the Wh, then divide by 12 V for Ah |

Average draw. This is not the rated power on the listing. A fridge’s compressor cycles on and off. Dometic rates the CFX3 45 at 8.2 A maximum input but publishes an average of 1.03 Ah/h at 90°F outside and 39°F inside. Runtime math uses the average. Our [power consumption explainer](https://portablefridgeguide.com/posts/portable-fridge-power-consumption-explained/) covers why the two numbers differ so much.

## Why does outside temperature change the answer?

A fridge works harder the bigger the gap between the air outside and the set temperature inside. Our calculator scales a published draw in a straight line with that gap. At 70°F outside and 37°F inside, the gap is about two-thirds of the gap at 90°F, so the draw is about two-thirds too. Real compressors do a little worse than linear in serious heat, so treat every scaled figure as an estimate.

Here is Dometic’s published CFX3 45 figure scaled to three outdoor temperatures, with the fridge set to 37°F:

  How long a battery runs a 45-quart fridge Estimated hours with no recharging, fridge set to 37°F, lid mostly closed. Based on Dometic's published 1.03 Ah/h for the CFX3 45 at 90°F, scaled by temperature.

| Battery | 70°F outside | 85°F outside | 100°F outside |
| --- | --- | --- | --- |
| 100 Ah AGM / lead-acid | 3.1 days | 2.1 days | 39 hr |
| 50 Ah LiFePO4 | 2.8 days | 46 hr | 35 hr |
| 100 Ah LiFePO4 | 5.6 days | 3.8 days | 2.9 days |
| 1,000 Wh power station | 4.4 days | 3.0 days | 2.3 days |

  Usable capacity: lead-acid/AGM 50%, LiFePO4 90%, power station 85%. At 85°F the same fridge needs roughly 80 W of solar with 5 peak sun hours to break even. Your fridge, your settings: [run the calculator](https://portablefridgeguide.com/tools/battery-runtime-calculator/).

## Worked example 1: a 45-quart fridge on a 100 Ah battery

Start with Dometic’s CFX3 45, a typical 45-quart single-zone fridge with a published draw:

- Published draw: **1.03 Ah/h** at 90°F outside, 39°F inside.

- Set it to 37°F instead and the gap grows slightly, giving about **1.08 Ah/h**.

- **100 Ah AGM:** 50 usable Ah ÷ 1.08 ≈ **46 hours**, just under two days.

- **100 Ah LiFePO4:** 90 usable Ah ÷ 1.08 ≈ **83 hours**, about three and a half days.

Now cool the weather to 70°F. The draw falls to about 0.67 Ah/h, and the same LiFePO4 battery lasts about 133 hours, or 5.6 days. At 100°F it rises to about 1.29 Ah/h, and runtime drops to about 70 hours. The battery is the same in all three cases. Only the weather changed.

That’s also why lithium is the usual upgrade for a fridge battery. A 100 Ah AGM and a 100 Ah LiFePO4 have the same label, but the lithium one gives you nearly twice the usable energy. The [LiTime 12V 100Ah LiFePO4](https://www.amazon.com/dp/B0BJ78JZ2B?tag=portablefridgeguide.com-20) on our accessories list is the common example, at about 1,280 Wh.

## Worked example 2: a fridge with its own battery

The [EcoFlow GLACIER Classic 35L](https://portablefridgeguide.com/fridges/ecoflow-glacier-classic-35/) is the one fridge in our data with a published fridge-mode draw: 0.57 Ah/h (165 Wh a day) at 77°F outside and 39°F inside, in Eco mode.

- 0.57 Ah/h × 12 V ≈ **6.8 W** average.

- 298 Wh battery ÷ 6.8 W ≈ **44 hours**.

EcoFlow claims up to 43 hours on that battery, so its own figures are consistent. That also suggests nearly all of the 298 Wh is usable. Scale the draw to 90°F outside and 37°F inside and it rises to about 0.80 Ah/h (9.6 W), so the same battery lasts about 31 hours. That’s the number we’d plan a hot weekend around.

The [Anker EverFrost 2 40L](https://portablefridgeguide.com/fridges/anker-everfrost-2-40/) is similar. Anker claims up to 52 hours on one 288 Wh battery and 4.3 days on two, measured empty, in Eco mode, at 39°F inside and 77°F outside. An empty fridge on a mild day is a best case. Treat it as a ceiling, not a plan.

## Worked example 3: when real use beats the spec sheet

Lab figures assume a closed lid and steady conditions. Camping isn’t that. Gnomad Home logged the [ICECO VL45 ProS](https://portablefridgeguide.com/fridges/iceco-vl45-pros/)’s smaller sibling, the VL35 ProS, for 123 hours of real camping. It averaged about 508 Wh a day, or roughly 1.76 A.

- Our capacity-based estimate for the VL45 ProS at 90°F/37°F: about **0.96 Ah/h**. On a 100 Ah LiFePO4, that’s 90 ÷ 0.96 ≈ **94 hours**.

- At Gnomad’s real-world average of 1.76 A: 90 ÷ 1.76 ≈ **51 hours**.

That’s nearly a 2× gap. It isn’t a flaw in either number. Gnomad’s figure includes everything a real trip throws at a fridge, and it’s for a different (smaller) box than ours. Use the spec-based figure as the best case and plan with a margin. If your trip involves hot afternoons, a lot of lid opening or warm groceries, assume the real-world end.

## Worked example 4: a power station

Power stations are rated in watt-hours. To use the formula, take the 85% usable share of the watt-hours, then divide by 12 V (the voltage the fridge’s Ah/h figure is quoted at):

- **1,000 Wh power station:** 1,000 × 0.85 = 850 Wh usable ÷ 12 V ≈ **71 usable Ah**.

- With the 45-quart fridge at 90°F outside (1.08 Ah/h): 71 ÷ 1.08 ≈ **66 hours**.

Run the fridge from the power station’s 12 V DC outlet, not its AC inverter. The inverter has its own losses. Small DC-only units like the [Anker SOLIX C300 DC](https://www.amazon.com/dp/B0D62PMB3R?tag=portablefridgeguide.com-20) (288 Wh) are a night or so for a small fridge. Our [powering guide](https://portablefridgeguide.com/posts/how-to-power-a-portable-fridge/) covers the options.

## What about the car’s starter battery?

We don’t give runtime numbers for starter batteries. The amp-hour rating isn’t what decides when the fridge stops. Battery protection is. Its job is to switch the fridge off while the battery still has enough charge to crank the engine, and Dometic’s CFX5 manual says to switch the fridge off, or move to a house battery, if the engine will be off for a long time. Expect a few hours to a night. Our [battery protection settings guide](https://portablefridgeguide.com/posts/portable-fridge-battery-protection-settings/) explains the cut-off levels.

## How do you get more hours from the same battery?

- **Pre-cool at home on AC** and load cold or frozen food. Pulling warm food down is the most power-hungry thing a fridge does.

- **Keep it out of the sun** and give the vents room to breathe. See our [hot weather tips](https://portablefridgeguide.com/posts/portable-fridge-hot-weather-tips/).

- **Set 37–39°F, not 32°F.** Dometic recommends 39°F for refrigeration and notes that even small changes in set temperature affect consumption.

- **Use Eco mode** once it’s cold, if your fridge has one.

- **Keep it full** and open the lid less often.

- **Measure.** A shunt monitor like the [Victron SmartShunt](https://www.amazon.com/dp/B0BF636VBX?tag=portablefridgeguide.com-20) shows what your fridge actually draws, which beats any estimate.

## Bottom line

Divide usable amp-hours by average draw, then adjust for heat and real life. A 45-quart compressor fridge on a 100 Ah LiFePO4 battery is a three-to-five-day setup in mild weather and a two-to-three-day setup in a heat wave. A built-in 300 Wh battery is about a day. If you want longer, add [solar](https://portablefridgeguide.com/posts/solar-panel-size-for-12v-fridge/) or a bigger battery. Then run your own numbers in the [battery runtime calculator](https://portablefridgeguide.com/tools/battery-runtime-calculator/).

## Don't guess. Calculate.

- [🎯 Fridge Matcher](https://portablefridgeguide.com/tools/fridge-matcher/): which fridges fit your trip
- [🔋 Battery Runtime](https://portablefridgeguide.com/tools/battery-runtime-calculator/): hours per charge and solar needed
- [🧊 Fridge vs Ice](https://portablefridgeguide.com/tools/fridge-vs-ice-cost/): how fast it pays back
- [📊 Compare every fridge](https://portablefridgeguide.com/fridges/): sortable spec table

## Frequently asked questions

### How long will a 100Ah battery run a 12V fridge?
For a typical 45-quart compressor fridge at 37°F inside, scaled from Dometic's published CFX3 45 figure: about 3.5 days from a 100 Ah LiFePO4 battery at 90°F outside, or about 2 days from a 100 Ah AGM battery, because you should only use half of an AGM's capacity. Cooler weather stretches that a lot, while heavy lid opening and freezer settings shorten it.

### How long will a car battery run a portable fridge?
Only a few hours to a night, and that's by design. A fridge's battery protection should switch it off while the starter battery still has enough charge to start the engine. For overnight running with the engine off, use a second battery or a power station.

### How long will a 300Wh power station run a fridge?
Roughly a day. EcoFlow rates its GLACIER Classic 35L at up to 43 hours on its 298 Wh battery at 77°F, which matches its published 0.57 Ah/h draw. In 90°F weather we'd plan on closer to 30 hours, and less for a bigger or less efficient fridge.

### Why does my fridge run out of battery faster than the calculator says?
Usually because of heat, sun on the fridge, frequent lid opening, warm food going in, a colder set temperature, or voltage drop tripping the battery protection early. The math assumes a steady fridge with the lid mostly closed.

## Sources

- [Dometic CFX3 45 product page and FAQ](https://www.dometic.com/en/product/dometic-cfx3-45-9600025318) · checked 2026-10-30 — 1.03 Ah/h at 32°C ambient and 4°C inside; runtime = usable Ah ÷ average Ah/h; usable capacity about 50% lead-acid, 80% NMC, near 100% LiFePO4
- [EcoFlow GLACIER Classic product page and spec table](https://us.ecoflow.com/products/glacier-classic-portable-refrigerator) · checked 2026-10-30 — Refrigeration (4°C/39°F): 165 Wh/24 h, 0.57 Ah/h; up to 43 h on the 298 Wh battery (35L), tested at 25°C/77°F ambient in Eco mode
- [Anker SOLIX EverFrost 2 40L product page](https://www.ankersolix.com/products/everfrost-2-40l-electric-cooler) · checked 2026-10-30 — 52 h on one 288 Wh battery and 4.3 days on two, empty cooler, Eco mode, 39°F inside, 77°F ambient

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Our #1 pick
 The only fridge we track with a published fridge-mode draw: 0.57 Ah/h at 77°F ![EcoFlow GLACIER Classic 35L](https://portablefridgeguide.com/_astro/ecoflow-glacier-classic-35.BOvSiZZQ_1BQs2x.webp)

### [EcoFlow GLACIER Classic 35L](https://portablefridgeguide.com/fridges/ecoflow-glacier-classic-35/)
 7.6

- 37 qt
- Single zone
- Down to -4°F
- Battery included
EcoFlow power-station owners who want a cordless fridge with a published, low average draw and IPX4 weather resistance.
[Check price on Amazon](https://www.amazon.com/dp/B0F62HMKBX?tag=portablefridgeguide.com-20)[Read the full review](https://portablefridgeguide.com/fridges/ecoflow-glacier-classic-35/)

[🔋 Will your battery last? Runtime and solar needs for your fridge, battery and weather.](https://portablefridgeguide.com/tools/battery-runtime-calculator/)[📊 Compare every fridge Sortable chart of every fridge we track.](https://portablefridgeguide.com/fridges/)

## Keep reading
[Power
### How to Power a Portable Fridge: Car Socket, Second Battery, Power Station or Solar
Five ways to power a 12V fridge: car socket, starter battery with battery protection, second battery and DC-DC charger, power station, and solar, compared.
 Updated Oct 30, 2026](https://portablefridgeguide.com/posts/how-to-power-a-portable-fridge/)[Explainer
### Portable Fridge Power Consumption Explained: Watts, Ah/h and Wh per Day
Why a 60 W fridge doesn't use 60 W: rated input vs average draw, Ah/h vs Wh, duty cycle, what independent tests measured, and why our chart is estimated.
 Updated Oct 30, 2026](https://portablefridgeguide.com/posts/portable-fridge-power-consumption-explained/)[Solar
### What Size Solar Panel Do You Need for a 12V Fridge?
How many watts of solar a 12V fridge needs: daily Wh divided by peak sun hours and losses, with worked examples for small, 45-quart and dual-zone fridges.
 Updated Oct 30, 2026](https://portablefridgeguide.com/posts/solar-panel-size-for-12v-fridge/)

 The only fridge we track with a published fridge-mode draw: 0.57 Ah/h at 77°F Glacier Classic 35L $$$$ Premium Price tier: Premium
[Check price](https://www.amazon.com/dp/B0F62HMKBX?tag=portablefridgeguide.com-20)