Using a 12V Battery for Your Fridge During a Power Outage

A 12V battery backup for your fridge keeps the fridge running through a power outage. Without power, the FDA's page on food and water safety during power outages and floods says "The refrigerator will keep food cold for about 4 hours if it is unopened", and it says to "Discard any refrigerated perishable food (such as meat, poultry, seafood, milk, eggs, or leftovers) that has been at refrigerator temperatures above 40°F for 4 hours or more." A 12V battery with an inverter can keep your fridge running for 10 to 40 hours depending on the battery size and chemistry: at 80% depth of discharge and through an inverter at 90% efficiency (an assumption for illustration, not a measured figure), a 50Ah LiFePO4 bank at 12.8V gives about 461Wh (50 × 12.8 × 0.80 × 0.90) and runs about 10 hours at 46W, the average of the top-freezer column the DOE labels less efficient, and a 200Ah bank gives about 1,843Wh and runs about 40.

This guide covers what you need, how to set it up, and how long different battery sizes will actually last with real fridge power data.

How Much Power Does a Fridge Actually Use?

Refrigerators do not draw constant power. A compressor fridge cycles on and off, and how much of each hour it runs depends on the ambient temperature, the thermostat setting and how often the door opens. The nameplate prints an electrical rating, not the compressor's running draw: GE lists 120V, 60Hz and 15A for the GTS18DCPRBB, the top-freezer this guide uses as its example. Average consumption over a full day is much lower because the compressor runs for only part of each hour.

The average wattage column is what matters for battery runtime calculations. A top-freezer refrigerator averages about 41-46W: the US Department of Energy lists 404 kWh a year for an 18.1 cu ft top-freezer in the column it labels less efficient, about 46W, and 363.5 kWh for an ENERGY STAR model, about 41W. The 12V DC row is Dometic's own print: 1.11 amp-hours per hour at 12V for its CFX5 35, which is 13.3W average and about 0.32 kWh a day. Dometic prints that figure for 90°F outside and 39°F inside the fridge (1.11Ah/h × 12V = 13.3W), and the same CFX5 35 page prints a rated input current of 7.6A at 12V, a rating rather than the average draw.

To measure your specific fridge, plug a kilowatt-hour meter (like a Kill A Watt) into the wall outlet and run it for 24 hours. Divide the kWh reading by 24 to get average watts. This gives you the most accurate number for battery sizing. Alternatively, check the yellow EnergyGuide label on your fridge: it lists annual kWh, which you can divide by 365 to get daily kWh, then by 24 for average watts.

Choosing the Right Battery

For a power outage fridge backup, you need a deep cycle battery, not a car starting battery. Starting batteries deliver high current in a short burst (engine cranking) but are not designed for sustained discharge. Deep cycle batteries deliver moderate current for hours, which is exactly what a fridge needs.

LiFePO4 is the best choice for dedicated fridge backup. At 80% depth of discharge, a single 100Ah 12V LiFePO4 battery provides about 922Wh of usable energy through the same 90% inverter (100Ah × 12.8V × 0.80 × 0.90), using the nominal voltage Victron's LiFePO4 datasheet prints, 12.8V. That powers a top-freezer fridge at the DOE's less-efficient figure of about 46W (404 kWh a year divided by 8,760 hours) for roughly 20 hours. Use the battery runtime formula to verify the math for your specific fridge. Two batteries extend that to about 40 hours, most of a two-day outage.

Lead-acid/AGM works but delivers less runtime per battery. At 50% DoD, a 100Ah 12V flooded lead-acid battery gives about 540Wh through the same 90% inverter (100Ah × 12.0V × 0.50 × 0.90) and runs about 12 hours on a 46W average fridge load (540 / 46 = 11.7). The 90% is this guide's example figure: Victron's datasheet prints maximum efficiencies of 92 to 95% across its 1200 to 5000 VA inverters, Renogy prints over 90% efficiency for its 2000W inverter, and your own inverter's datasheet prints yours. It is not simply half the lithium figure, because it starts from 12.0V rather than 12.8V and you stop at half its capacity rather than 80%. You need about 1.7 times the lead-acid capacity to match LiFePO4 runtime (922 / 540 = 1.7). That gap starts at the label: see the stored watt-hours in a 12V battery for the two chemistries side by side. For a detailed comparison, see our LiFePO4 vs lead-acid guide.

Use the 12V battery fridge calculator to see exact runtime for your battery size and fridge wattage.

Sizing the battery for your specific fridge

To calculate the exact battery capacity you need, start with your fridge's average wattage (from the EnergyGuide label or a Kill A Watt meter). Multiply by the hours of backup you want, then account for inverter losses and depth of discharge.

For example, take GE's GTS18DCPRBB, the 18.0 cu ft top-freezer we picked for this example. Its EnergyGuide label prints 482 kWh a year, which averages out to 55W across the 8,760 hours in a year (482,000 Wh / 8,760 h = 55W). We assume 24 hours of desired backup and a LiFePO4 battery at 80% DoD. We also assume a 90%-efficient inverter; Renogy prints over 90% efficiency for its 2000W 12V pure sine wave inverter:

Required capacity = (55W × 24h) / (0.90 efficiency × 12.8V × 0.80 DoD) = 1,320 / 9.216 = 143 Ah

The solar battery bank size calculator returns the same 143 Ah for 1,320 Wh a day, one day of autonomy, 12V LiFePO4, 80% depth of discharge and 90% inverter efficiency. A 200Ah LiFePO4 battery gives you comfortable margin above the minimum. Say a larger fridge averages 80W, with the same 24-hour target: (80 × 24) / (0.90 × 12.8 × 0.80) = 208 Ah, which the calculator also returns for 1,920 Wh a day at the same settings. That pushes you to either a single 300Ah battery or two 200Ah batteries in parallel.

If your target is shorter, say 8 to 12 hours, a single 100Ah LiFePO4 battery covers it for both figures in this guide: its 922Wh lasts about 17 hours at the GE example's 55W and about 20 hours at the DOE's less-efficient 46W. The key is knowing your fridge's actual average consumption, not the nameplate rating. Using the wrong number leads to either an oversized battery you did not need or an undersized one that runs out mid-outage.

Setting Up a Battery Backup for Your Fridge

A basic fridge backup system has three components: battery, inverter, and cables. Our guide to choosing an inverter size shows where a maker prints the continuous and surge ratings.

1. Battery. A 100Ah 12V LiFePO4 battery provides about 20 hours of fridge runtime at the DOE's less-efficient average of 46W. For 24+ hours, use 200Ah or two 100Ah batteries in parallel. Keep the battery in a ventilated area (not required for LiFePO4 but good practice) near the fridge location to minimize cable length.
2. Inverter. A refrigerator requires a pure sine wave inverter - modified sine wave inverters can damage compressor motors and cause humming or overheating. Size the inverter for the compressor startup surge, not average draw. Embraco prints a locked-rotor amperage of 10.2A for its EM3D60HLT household compressor, which is roughly 1,170W at 115V; that is the figure the inverter's surge rating has to clear. No datasheet we opened prints how long the surge lasts, so treat any published duration with suspicion. Pick a pure sine wave inverter whose surge rating clears that figure and whose continuous rating clears the fridge's running draw. Do not oversize: an inverter draws power with no load at all, and Victron's datasheet prints a zero-load power at 12V of 20W for its 3000 VA model against 8W for its 1200 VA model, beside the example's 55W average load.
3. Cables. Use appropriately sized cables between the battery and inverter. A 1,000W inverter at its full rating on a 12V battery, through the 90% example efficiency, draws about 93A (1,000 / (12 × 0.90) = 92.6). Undersized cables cause voltage drop that reduces inverter efficiency and can overheat. For that 1,000W inverter on 12V at 90% efficiency and a 3% maximum voltage drop, with continuous duty sized at 125%, the inverter cable sizing calculator returns 1/0 AWG for a one-way run of 3 feet and of 6 feet, and 2 AWG for both with continuous duty switched off, at its default setting of terminals not marked for 75°C. Where the inverter's DC terminals are marked for 75°C, it returns 1 AWG for both runs with continuous duty on and 3 AWG with it off.
4. Connection. Connect battery to inverter with properly crimped or soldered ring terminals. Plug the fridge into the inverter's AC outlet. The fridge does not know or care that it is running on battery: it sees standard 120V AC power from the inverter, same as the wall outlet.
5. Recharging. After the outage, recharge the battery using a compatible smart charger from a wall outlet. LiFePO4 batteries need a charger with a LiFePO4 setting. A 20A charger puts 100Ah back into a flat 100Ah LiFePO4 battery in about 5 hours at its full current (100Ah / 20A = 5), before any taper at the end of the charge. Model your own numbers with the battery charge and discharge calculator, and a smaller charger stretches the job a long way: our charge time by charger amps guide runs the same 100Ah battery at a range of charger currents. If outages are frequent, consider adding a solar panel for daytime recharging. Even a 100W panel provides meaningful supplemental charge during the day.

Runtime Estimates by Battery Size

These estimates use the worked example's fridge, GE's GTS18DCPRBB, at the 55W its EnergyGuide label works out to (482 kWh a year), with a pure sine wave inverter at the 90% example efficiency: LiFePO4 batteries at 12.8V and 80% DoD in the first four rows, and flooded lead-acid at 12.0V and 50% DoD in the last two. For the lead-acid rows, 100 × 12.0 × 0.50 × 0.90 = 540 Wh and 540 / 55 = 9.8 hours, and 200 × 12.0 × 0.50 × 0.90 = 1,080 Wh and 1,080 / 55 = 19.6 hours.

If your fridge is larger and its own label works out higher, say 75W or 90W, divide the usable energy by that figure instead. A 100Ah LiFePO4 battery then lasts about 12 hours at 75W and about 10 hours at 90W, against about 17 hours at the example's 55W.

Extending Your Backup Runtime

Keep the fridge door closed. Every time you open the door, cold air escapes and the compressor must run longer to recover. The FDA's page linked above says to "Keep the refrigerator and freezer doors closed as much as possible to maintain the cold temperature." Beside the refrigerator's "about 4 hours if it is unopened", it prints that "A full freezer will keep the temperature for approximately 48 hours (24 hours if it is half full) if the door remains closed", and it says to check "that the freezer temperature is at or below 0° F, and the refrigerator is at or below 40° F."

Turn off the ice maker. Automatic ice makers draw extra power and are unnecessary during an outage. Disconnect or disable them to reduce the fridge's average consumption.

Set the fridge to a slightly warmer temperature. A warmer setting shortens the compressor's run time and extends battery life. The figure the FDA's page prints for a refrigerator is "at or below 40° F", so the setting stays at or below that.

Pre-chill before the outage. If you have warning (hurricane forecast, planned utility maintenance), set the fridge to its coldest setting ahead of time and fill any empty space with water bottles. The thermal mass of cold food and water keeps the fridge colder longer, reducing compressor run cycles once you switch to battery power.

Consider a dedicated 12V DC fridge. A 12V DC compressor fridge (like those used in RVs and boats) connects directly to the battery without an inverter, eliminating the inverter loss; for appliances run through an inverter, Victron prints "add about 10-15% extra for any 230V appliances, like the laptop charger", so its own example is a 230V laptop charger. For a dedicated emergency backup, a small 12V fridge running directly from a battery bank is the most efficient option. Use the battery runtime calculator to compare DC vs AC fridge runtime on the same battery.

Add a small solar panel. A single solar panel connected to a charge controller adds charge on every day with sun. At 5.18 peak sun hours a day, the annual average that NLR's PVWatts prints for a roof-mounted array at a 39° tilt in Kansas City, and 14% system losses, the solar panel output calculator returns 404 Wh a day for one 100W panel and 807 Wh for one 200W panel. Against the 1,467 Wh the GE example's fridge draws from the battery in a day (55W × 24h / 0.90), that is about 28% and 55% of the day's draw (404 / 1,467 and 807 / 1,467), so the panel slows the drain rather than replacing the battery. The solar battery charge time calculator takes your battery's capacity, voltage, chemistry and depth of discharge, your total solar wattage, peak sun hours, system losses and charge efficiency, and returns the days of sun needed to refill the battery, with the daily solar watt-hours and the watt-hours to replace.

Combine with a generator for extended outages. For multi-day blackouts, a battery bank paired with a small propane generator covers you around the clock: charge the battery during the day, run the fridge on battery overnight. Our propane generator runtime guide explains fuel planning and runtime estimates for this hybrid approach.