What is a refrigerator duty cycle?

The duty cycle is the share of each hour the compressor actually runs. A fridge rated at 150W does not draw 150W without stopping: the compressor cools the box, shuts off, and waits for the temperature to drift back up. No manufacturer publishes a duty-cycle percentage, so we derive one from two figures that are printed. Dometic gives 1.11 amp-hours per hour for its CFX5 35 at a 90F ambient, which is 13.3W at 12V, and Secop gives 36.7W running for its BD35F compressor; 13.3 divided by 36.7 is 36%, and that is the default on this page. Read it with its condition attached: it comes from one fridge and one compressor at a 90F ambient, so a cooler kitchen runs below it. One caveat we will not hide either: Dometic does not print which compressor is inside that cooler, so the pairing assumes a BD35F-class unit at the slowest speed Secop prints.

Can a 12V battery run a full-size household refrigerator?

Yes, with an inverter and a real battery behind it. The DOE publishes two figures for an 18.1 cu ft top-freezer tested to 10 CFR 430: 363.5 kWh a year for an ENERGY STAR model and 404 kWh for a less efficient one, which work out at 41.5W and 46.1W average. At 46W a 100Ah 12V LiFePO4 bank runs about 20 hours through a 90% inverter, and a 200Ah bank about 40. The starting surge is the part that catches people out: Embraco prints a locked-rotor amperage of 10.2A for its EM3D60HLT household compressor, roughly 1,170W at 115V, so the inverter's surge rating has to clear that. No datasheet we opened prints how long the surge lasts, so we do not quote a duration.

Is a 12V DC fridge better than an AC fridge on an inverter for battery power?

A 12V DC fridge skips the inverter, and that is worth about 11% more runtime on the same battery: dividing by 0.90 instead of 1.00 is where the difference comes from. Victron prints 87-91% as the best efficiency its small Phoenix inverters reach, and its own measured curve for a 3kVA unit reads 71.3% at a 50W load, so the loss on a fridge-sized draw can be larger than the headline figure suggests. The trade-off is price and size: 12V compressor fridges run $300-1,000 as of early 2026 for a Dometic or Engel, and hold far less than a residential unit. Prices and rates on this page are our own estimates as of the date shown; they change often. Enter your own figures for a current result. For an occasional outage, an inverter and the fridge you already own is the practical answer.

12V Battery Fridge Runtime Calc — Duty Cycle & Watts

7 min read

A fridge compressor runs in bursts, so the number on the rating plate is not the number your battery sees. This 12V battery fridge runtime calculator takes the compressor's running watts and the share of the hour it actually runs, then discharges your bank at that average. Pick your chemistry and it uses the discharge behaviour that chemistry's makers print, instead of assuming every battery hands back its full rating at every rate. Already have a maker's average figure, in amp-hours per hour or kilowatt-hours per year? Enter that as the watts and set duty cycle to 100. For outage planning and wiring, see our 12V fridge battery guide.

Fridge runtime on 100Ah 12V batteries comparing LiFePO4 and flooded lead-acid at a 46W draw.

What Number to Enter for Fridge Watts

Getting this one field right matters more than everything else on the page. A refrigerator's rating plate carries the maximum current the unit may draw, not what the compressor pulls while it runs, and not the average over an hour. Dometic prints both figures for the same cooler: the plate says 7.6A at 12V, which is 91W, while the product page prints an energy consumption of 1.11 Ah/h at a 90F ambient, which is 13.3W. Enter the plate figure and your runtime comes out roughly seven times too short.

So either enter the compressor's running watts and a duty cycle, or take the maker's average and set duty cycle to 100. Both routes appear below, with the printed figure each one starts from.

What the maker prints	Printed figure	Enter it as	Runtime, 100Ah 12V LiFePO4
Dometic CFX5 35, energy use at 90F ambient	1.11 Ah/h = 13.3W average	13W at 100% duty	2 days 23 hours
Secop BD35F, 12V power at 2,000 rpm, -10C evaporating	36.7W running	37W at 36% duty	2 days 21 hours
DOE FEMP, 18.1 cu ft top-freezer, ENERGY STAR	363.5 kWh/yr = 41.5W average	42W at 100% duty	21 hours 57 minutes
DOE FEMP, same fridge, less efficient model	404 kWh/yr = 46.1W average	46W at 100% duty	20 hours 2 minutes
Embraco EM3D60HLT household compressor, AHRI rated point	74W running	74W at 36% duty	34 hours 36 minutes

The runtime column runs every row on a 100Ah 12V LiFePO4 bank at 80% depth of discharge and 90% system efficiency, this page's defaults. LiFePO4 counts at the 12.8V nominal Victron prints, so 100Ah is 1,280Wh rather than 1,200Wh. Skipping the inverter and wiring a DC fridge straight to 12V removes that 90% step, which is 11% more runtime on the same battery. A lead-acid bank of the same rating gives back less as you pull harder, which is why the chemistry selector changes the answer and not just the label. Our lead-acid battery runtime calculator shows the same effect on a bigger load.

LiFePO4 fridge runtime chart from 50Ah to 200Ah at a 46W average draw through a 90% inverter. — A 200Ah LiFePO4 bank runs the 46W average DOE prints for an 18.1 cu ft top-freezer for about 40 hours.

Example: Keeping a Fridge Running During a Power Outage

The power goes out and the kitchen fridge has to keep running. Its plate says 150W. At the 36% duty this page derives, the average draw is 150 x 0.36 = 54W. That sits a little above the 46W the DOE publishes for an 18.1 cu ft top-freezer, which is the check worth doing on any plate figure.

You have a 200Ah 12V LiFePO4 battery and a 1,000W pure sine inverter at 90%. Victron prints 12.8V nominal for LiFePO4, so the bank holds 200 x 12.8 = 2,560Wh. At 80% depth of discharge and 90% inverter efficiency: 200 x 12.8 x 0.80 x 0.90 = 1,843.2Wh at the outlet.

Runtime: 1,843.2 / 54 = 34.1 hours, which this calculator prints as 34 hours 8 minutes. That covers a long outage with room left.

Keeping the door shut is the one lever that reliably helps, because every opening dumps cold air the compressor then has to replace. Pre-cooling and thermal mass work the same way. Nobody publishes a figure for how much they buy you, so we do not print one.

Worked Examples

Keeping Food Cold During a 24-Hour Power Outage

Context

A full-size fridge draws 150W while the compressor runs and runs about 36% of the hour, so 54W average. Behind it sits a 200Ah flooded lead-acid bank and a pure sine inverter at 90%, held to the 50% depth Trojan recommends.

Calculation

Average load: 150 x 0.36 = 54 W

Current from the bank: 54 / 0.90 / 12 = 5.0 A, which is 0.025 of the 200Ah twenty-hour rating

Trojan's printed discharge points put a full discharge at that rate near 42 hours; half of it, at 50% depth, is 21 hours

Interpretation

About 21 hours. Not the full day, and the door is the variable that decides how close you get: every opening raises the duty cycle. The identity most calculators use would have promised 20 hours here, and at a harder load it would have promised far more than the battery delivers.

Takeaway

For a full 24 hours you want either more bank or a panel topping it up through the afternoon. Size the panel with our solar panel output calculator.

A 12V Portable Fridge from the Maker's Own Figure

Context

A Dometic CFX5 35 in the back of a van, wired straight to a 100Ah LiFePO4 battery with no inverter. Dometic prints its energy use rather than a wattage: 1.11 amp-hours per hour at a 90F ambient with the box at 39F.

Calculation

Average draw: 1.11 Ah/h x 12V = 13.3W, entered as 13W with duty cycle at 100

Bank energy: 100 x 12.8 = 1,280 Wh at the nominal voltage Victron prints

Usable at 80% depth, no inverter: 1,280 x 0.80 x 1.00 = 1,024 Wh

Runtime: 1,024 / 13 = 78.8 hours, which the calculator prints as 3 days 7 hours

Interpretation

Three days and change, on one 100Ah battery. Feed the same fridge in through its rating plate instead, at 7.6A and 12V, and the answer collapses to about eleven hours. The fridge did not change; the number you typed did.

Takeaway

When the maker prints an average, use it and set duty cycle to 100. For the rest of a van or RV electrical budget, our RV battery runtime calculator handles the other loads.

Frequently Asked Questions

Glossary

Compressor Duty Cycle

The share of each hour the fridge compressor actually runs. A 36% duty cycle means the motor runs about 22 minutes per hour. Heat, frequent door opening and warm food all push it up, which is why the same fridge empties a battery faster in a summer garage than in a kitchen.

Average Power Draw

The effective continuous wattage: compressor watts multiplied by the duty cycle fraction. A 150W fridge at 36% duty averages 54W, and that is the number battery sizing runs on. Makers who print amp-hours per hour or kilowatt-hours per year are giving you this figure directly.

Modified vs Pure Sine

Modified sine inverters are cheaper and produce a stepped approximation of mains AC rather than a smooth wave. Pure sine inverters produce a wave like the grid's, and manufacturers of motor-driven appliances generally specify them. We have not found a manufacturer figure for how much a modified wave costs a fridge compressor, so this page does not model a penalty.

Adding solar to keep your fridge running indefinitely? The solar battery count calculator sizes a complete off-grid system.

Two numbers decide this calculation: what the compressor really draws while it runs, and how much of the hour it runs. The first is on a datasheet, not a rating plate. The second nobody publishes, so we derive 36% from Dometic's and Secop's printed figures and ship that as the default, with the condition attached: one fridge, one compressor, a 90F ambient. A warm garage sits near it and a cool basement below it. A plug-in energy meter on your own fridge for 24 hours beats both routes: divide the kWh reading by 24, multiply by 1,000, and enter that as the watts with duty cycle at 100. If you want the fridge to run indefinitely, the solar panel and battery sizing calculator sizes an array that refills the bank faster than the fridge empties it.

More Battery calculators

Browse all battery calculators — LiFePO4, lead-acid, AGM, and lithium-ion runtime, charge time, and capacity sizing.

Last updated: September 22, 2026

Written and maintained by Dan Dadovic, Commercial Director at Ezoic Inc. & PhD Candidate in Information Sciences. He works professionally as Commercial Director at Ezoic Inc., leading revenue strategy across digital publishing.

Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.

Methodology reviewed by Doc. dr. sc. Damir Topić, Assistant Professor, FERIT Osijek.