How the math works
A battery's usable energy is its rated amp-hours times how deeply you can safely discharge it: about 90% for lithium iron phosphate (LiFePO4), about 50% for AGM or flooded lead-acid. Divide that by everything you draw in a day and you get days of runtime with no charging.
Solar adds back roughly panel watts × peak sun hours × 0.75 ÷ 12.8 amp-hours a day. The 0.75 covers heat, panel angle, wiring and charge-controller losses, which typically cost 20–30% of the nameplate rating. If solar covers your daily load, you can stay parked as long as the weather holds. If it doesn't, the battery covers the gap and the calculator shows how long it lasts.
The number that matters most: ambient temperature
A compressor fridge's daily draw can roughly double between a mild spring week and a parked-in-the-sun summer afternoon, because heat leaks in faster and the compressor runs longer to remove it. Manufacturer ratings are usually given at one test condition (Dometic quotes 90°F ambient). That's why this calculator uses three planning figures per fridge instead of one. Venting the compressor side of the fridge, keeping it out of direct sun and not opening the lid more than you need to are the cheapest efficiency upgrades there are.
Driving counts too
This calculator assumes you're parked. If you drive most days, a DC-DC charger from the alternator adds a lot: a 30A charger running for an hour puts back roughly 30Ah, which covers a typical fridge for a day. For the full power-system picture, including induction cooking, use the kitchen power calculator and the power budget guide. To choose a fridge, see the 12V fridge buying guide.
Where each fridge figure comes from
Daily figures are amp-hours at 12 V nominal. Manufacturer ratings are lab or stated test conditions; values marked estimate are our planning figures, not measurements.
| Fridge | Mild / warm / hot (Ah/day) | Source |
|---|---|---|
| Dometic CFX2 45 Fridge | 18 / 21 / 27 (hot: estimate) | No US energy figure is published. Derived from Dometic's Australian R600a model rating of 0.86 Ah/h at 32°C (90°F) ambient (~21 Ah/day, ~250 Wh/day), so the warm value already reflects hot-ish conditions; hot is an estimate. |
| Dometic CFX5 35 Fridge | 20 / 27 / 34 | Dometic's US rating of 1.11 Ah/h at 90°F ambient (~27 Ah/day) and the review's 30–35 Ah/day summer planning figure. |
| Iceco VL35 ProS 12V Fridge Freezer | 28 / 36 / 54 (hot: estimate) | ICECO's 0.430 kWh/24h figure (EnergyGuide label, 157 kWh/yr; ~36 Ah/day at 12 V) under standard test conditions. Both the mild and hot values are our estimates. |
| BougeRV CR 30Qt 12V Fridge | 27 / 33 / 55 (hot: estimate) | Rated 45 W ECO / 60 W MAX. Mild and warm match Footprint Hero's owner test (3 days on 100 Ah, ~27–33 Ah/day). Hot is our estimate from duty cycle in MAX mode; it can run higher. |
| Alpicool C20 12V Fridge | 26 / 30 / 50 (hot: estimate) | Alpicool publishes no rated wattage; its only energy claim is "1 kWh lasts 2–4 days" (~21–42 Ah/day, conditions not stated). Values are planning estimates. |
| ICECO JP40 Pro 12V Fridge | 28 / 35 / 55 | The review's duty-cycle estimate: 25–35 Ah/day mild to moderate, 50–60 Ah/day in hot conditions (ICECO's manual lists a 0.323 kWh/24h lab figure, ~27 Ah/day). |
| ICECO VL60 Dual Zone Fridge | 30 / 45 / 65 (hot: estimate) | ICECO's manual catalog page and Amazon listing give 0.545 kWh/24h (199 kWh/yr, ~45 Ah/day, both zones); a 0.416 figure in the manual's consumption table appears misaligned. Camp Addict's 24-hour run works out to roughly 50 Ah/day. Mild assumes one zone off or cool weather; hot is an estimate. |
| Dometic CFX3 35 Fridge | 18 / 24 / 31 (hot: estimate) | Dometic's US rating of 0.98 Ah/h at 90°F ambient and 39°F inside (~23.5 Ah/day, ~282 Wh/day at 12 V). Mild and hot values are our estimates. |
Frequently asked questions
How long will a 12V fridge run on a 100Ah battery?
On a 100Ah lithium (LiFePO4) battery you can use about 90Ah. A typical 35-40L compressor fridge uses roughly 20-35Ah a day in mild to warm weather, so expect about 2.5 to 4.5 days with no charging and nothing else running. On a 100Ah AGM battery you should only use about 50Ah, which cuts that to roughly 1.5 to 2.5 days. In hot weather, plan on the low end or less.
How long will a 12V fridge run on a 200Ah battery?
About 180 usable amp-hours on lithium. With a fridge at 25Ah a day plus 10Ah of other loads, that is around 5 days with no sun or driving. Add even 200W of solar in summer and most single-fridge setups break even and can stay parked indefinitely.
How many amp-hours does a 12V fridge use per day?
Most 35-45L compressor fridges use roughly 18-35Ah a day in mild to warm weather, and 30-55Ah or more in heat. Dual-zone fridges and larger boxes sit higher; ICECO rates its VL60 Dual Zone at 0.545kWh per 24 hours, about 45Ah. The biggest factors are ambient temperature, ventilation around the compressor, setpoint, and how often the lid opens.
Why does my fridge use so much more power in summer?
A compressor fridge only runs when the inside warms past its setpoint. The hotter the air around it, the faster heat leaks in and the longer the compressor runs to remove it, and a compressor in a hot, enclosed cabinet also works less efficiently. That is why summer planning figures are often 1.5 to 2 times mild-weather figures. Ventilating the compressor side matters more than any other installation detail.
Lithium or AGM for a fridge battery?
Lithium (LiFePO4) for almost everyone who runs a fridge full-time. You can use about 90% of its rated capacity versus about 50% for AGM, it weighs roughly half as much, and it holds voltage steadier, which helps avoid fridge low-voltage cutoffs. AGM still makes sense for occasional weekend use on a tight budget.
How much solar do I need to run a 12V fridge?
Divide your total daily watt-hours by peak sun hours, then allow for 20-30% losses. A 30Ah-a-day load is about 385Wh; with 4 peak sun hours that is roughly 96W of real output, or about 130W of panels after losses, so 150-200W gives you some margin. In winter or under trees, sun hours drop to 1-2 and you need roughly double that, or alternator charging.