A 12.8 V, 100Ah battery can run a refrigerator for about 19 hours in this worked example: a fridge using 1 kWh/day, 80% of battery capacity available, 90% inverter conversion efficiency and 8 W of additional inverter draw. Your answer can be very different. Use your fridge’s energy consumption—not its compressor wattage alone—to calculate it.
A fridge that survives a short power cut may still drain the battery before breakfast. The missing detail is often the energy used over a full day, or an inverter that stays awake all night. This guide helps you estimate both, check the assumptions and work out what must change for longer backup.
Calculate your runtime · Find your fridge energy use · Compare battery sizes · Plan solar recharging
Refrigerator battery runtime calculator
Start with your own measured kWh/day. Defaults below are a worked example, not a claim about your equipment. This estimate assumes no solar charging during backup.
Startup check remains separate: this tool estimates energy, not whether the inverter and battery can start your compressor. Check their continuous and surge ratings before relying on the result.
First, find the number that matters: kWh per day
Look for annual energy consumption on the refrigerator’s energy label or model documentation. A label showing 365 kWh/year gives a starting estimate of 1 kWh/day: 365 ÷ 365. A 548 kWh/year label gives about 1.50 kWh/day. Label values come from test conditions; a hot room, different settings and frequent door openings can change actual use.
For a better household estimate, record energy with a suitably rated plug-in energy meter over several representative days. Divide the measured kWh by the elapsed days. For example, 3.6 kWh over three days means 1.2 kWh/day. Include ordinary use and defrost cycles; repeat the measurement in hotter conditions if that is when you need backup. Follow the meter and appliance instructions, and leave hardwired measurements to a qualified person.
Do not multiply a compressor’s running watts by 24 unless it truly runs at that power continuously. Refrigerators cycle, and variable-speed models change output. An instantaneous 120 W reading is not the same thing as a 120 W average over a day. Virginia Tech’s appliance-energy guide explains the difference between operating wattage and energy over time.
The runtime formula, with every assumption visible
Available battery energy (Wh) = nominal volts × Ah × (starting charge − reserve) ÷ 100.
Average battery draw (W) = [(fridge kWh/day × 1,000 ÷ 24) + other average AC watts] ÷ inverter efficiency + additional inverter watts.
Runtime (hours) = available battery Wh ÷ average battery watts. Use efficiency as a decimal: 90% becomes 0.90. The reserve is the charge level where you plan to stop, not extra energy you can spend.
Here is the opening example step by step. Available energy is 12.8 × 100 × 0.80 = 1,024 Wh. Fridge demand averages 1,000 ÷ 24 = 41.67 W. Battery draw is 41.67 ÷ 0.90 + 8 = 54.30 W. Dividing 1,024 by 54.30 gives 18.9 hours. This calculated result, rather than an unqualified “one day” claim, is the number to use for these assumptions.
The 90% and 8 W inputs are example assumptions, not universal inverter specifications. Manufacturer data can list maximum efficiency and separate zero-load consumption; those figures do not necessarily describe your fridge’s operating point. Victron’s inverter specification table illustrates why both matter. If measured overall efficiency already includes idle losses, enter zero additional draw to avoid counting the loss twice.
100Ah vs 200Ah: refrigerator runtime comparison
These are calculated scenarios, not battery tests. Every row assumes a full battery, 1 kWh/day fridge consumption, 90% conversion efficiency, 8 W additional inverter draw, no other loads and no charging. The different reserves are illustrative choices; follow your battery’s documented operating limits.
| Battery example | Charge available | Energy available | Estimated runtime |
|---|---|---|---|
| 12 V, 100Ah lead-acid example | 100% to 50% | 600 Wh | 11.1 hours |
| 12.8 V, 100Ah LiFePO₄ example | 100% to 20% | 1,024 Wh | 18.9 hours |
| 12.8 V, 200Ah LiFePO₄ example | 100% to 20% | 2,048 Wh | 37.7 hours |
| 25.6 V, 100Ah LiFePO₄ example | 100% to 20% | 2,048 Wh | 37.7 hours |
The last two rows contain the same nominal energy even though their Ah ratings differ. Always compare watt-hours at the stated voltage. The lead-acid row is a simplified energy estimate: discharge rate can reduce usable capacity. Victron’s explanation of Peukert’s effect describes this limitation. This calculator does not model that effect, temperature, battery aging or voltage-triggered shutdown.
What changes if you need a full 24 hours?
Using the worked example, 24 hours requires 54.30 × 24 = 1,303 Wh above your reserve. At 12.8 V with 80% of capacity available, that is 1,303 ÷ (12.8 × 0.80) = 127.3Ah, or 128Ah when rounded up. This is the mathematical minimum under the assumptions, not a finished purchase specification.
Now test the conditions that worry you. At 1.3 kWh/day—30% more fridge energy—the same 100Ah battery lasts about 15.0 hours. Add a continuous 20 W AC load to the original example and runtime falls to about 13.4 hours. If the battery begins at 80% charge and you keep a 20% reserve, only 60% of nominal capacity is available; original-example runtime becomes about 14.1 hours.
This is why “my friend gets two days from 100Ah” is not a sizing method. Their fridge, voltage, inverter, starting charge and test conditions may all be different. Save those inputs alongside the reported hours when comparing systems.
Enough battery energy does not prove the compressor will start
Runtime and startup are separate checks. The inverter must support the refrigerator’s required voltage, frequency, continuous demand and starting surge. The battery and its management system must also supply the required current. A brief surge can trip equipment even when the energy calculation predicts many hours of operation.
Use the exact refrigerator and inverter documentation, including how long a surge rating is supported. Do not size an inverter from the 41.67 W average in our example: that is a daily energy average, not the compressor’s peak demand. An “inverter refrigerator” describes its compressor control; it does not automatically mean the appliance accepts a direct battery connection.
If you are checking a longer battery-to-inverter cable run, our voltage-drop calculator can help evaluate voltage loss. Cable ampacity, overcurrent protection and installation requirements still need separate checks.
How much solar is needed to put the energy back?
Battery capacity determines the energy you can store. Panels determine how quickly you can replace what you used. A larger battery alone does not solve a daily charging shortfall.
The worked example consumes about 1.303 kWh from the battery per 24 hours. As an illustrative recharge calculation, assume four peak-sun-hours and a separate 80% panel-to-stored-energy factor for the solar charging path. Required array power is 1,303 Wh ÷ (4 h × 0.80) = 407 W. With only two peak-sun-hours, it becomes about 815 W. These are energy-balance estimates, not guarantees that a 400 W or 800 W system will keep the fridge running.
Peak-sun-hours are equivalent full-output solar hours, not the number of daylight hours. Use location- and season-specific resource data, account for shading, and check controller limits and battery charging requirements. This recharge example counts a solar charging-path loss separately from the inverter discharge loss already included above. Avoid applying the same loss twice when using a different system model. For a worked daily-energy example, see whether a 200W solar panel can charge a 100Ah battery.
The University of Maryland’s solar sizing guide explains the relationship between energy demand, solar resource and system losses. For panel orientation planning, use our solar panel tilt calculator. A multi-day cloudy period needs its own backup plan; an annual average is not a promise of daily recharge.
A practical worksheet before you buy
| Write down | Where to find it | Why it changes the decision |
|---|---|---|
| Fridge kWh/day | Measured energy or annual label ÷ 365 | Sets the main energy demand |
| Nominal battery V and Ah | Exact battery datasheet | Converts storage into Wh |
| Starting charge and reserve | Your backup plan and battery limits | Defines energy you can actually spend |
| Conversion and standby losses | Inverter data or suitable measurements | Stops low-load runtime being overstated |
| Compressor startup requirements | Appliance and inverter documentation | Checks whether backup can start at all |
| Worst-season charging resource | Local solar data and shading assessment | Tests whether daily recharge is realistic |
Comparing a portable power station with a solar generator bundle? Write down two separate figures for each offer: usable AC energy in Wh and included panel capacity in W. Suppose two stations each deliver 800 Wh at the AC outlet under your intended load. A fridge averaging 50 W has an estimated 16 hours on either station from full charge with no sunlight. A 200 W panel bundled with one station adds no overnight capacity. For a next-day estimate, four equivalent full-sun hours at an assumed 75% net panel-to-battery yield would put about 600 Wh back into storage before subtracting ongoing loads. Check the station’s solar input limit and the panel’s voltage compatibility before counting on that recharge. If your packs come from EGO lawn tools, use the EGO Nexus battery-pack runtime table to compare your actual combination.
If your first estimate falls short, identify the biggest cause before buying more equipment. An unexpectedly high measured fridge kWh/day calls for checking appliance condition and usage. A large standby draw points toward inverter operation or sizing. A good battery that starts half-charged points toward the charging schedule. Each problem has a different remedy.
Frequently asked questions
Can a 100Ah battery run a refrigerator all night?
It can in some systems. In our 12.8 V example, estimated runtime is 18.9 hours from full charge to a 20% reserve. A hotter fridge, lower starting charge, extra loads or startup incompatibility can change the result. Enter your measured daily energy and battery specifications rather than assuming every 100Ah battery behaves alike.
How long will a 1,000Wh power station run a fridge?
First establish whether 1,000Wh is nominal battery energy or a measured usable AC output figure. For 1,000Wh nominal energy, 80% available, 90% conversion efficiency, 8 W additional draw and a 1 kWh/day fridge, the same model gives about 14.7 hours. If the manufacturer supplies usable AC energy measured under comparable conditions, divide that by the fridge’s average AC watts; do not subtract the same conversion losses again.
Will a 200 W solar panel run a refrigerator?
The panel wattage alone cannot answer that. In an illustrative four-peak-sun-hour day with an 80% charging-path factor, 200 W produces about 640 Wh of stored energy—less than the 1,303 Wh daily battery demand in our worked example. Different fridge demand and solar conditions change the balance, and storage is still needed when generation is unavailable.
Can I use this calculator for a DC camping fridge?
Only if you enter the fridge’s measured daily DC energy, set conversion efficiency to 100%, set additional inverter draw to zero and account separately for any other DC losses or loads. The default example describes an AC refrigerator powered through an inverter. Do not use an AC appliance label as if it described a different DC fridge.
How to use the result responsibly
Treat the result as a planning estimate and verify it with your actual equipment before an outage. It is not a food-temperature prediction, an electrical installation design or a product certification. This guide uses transparent calculations and linked technical sources; it does not claim hands-on testing of the equipment in the examples. See our editorial policy and disclaimer.
Already own EGO lawn-tool batteries? Compare refrigerator runtime with two or four EGO Nexus battery packs, including a ten-hour overnight example and a compressor startup check.
Measure first, then calculate
For a repeatable input, follow the refrigerator kWh measurement guide. It includes an overnight log and explains how to compare several readings instead of relying on compressor watts. Then use the 200W panel charging example to check whether the next day’s solar can replace the energy while the fridge continues running.