How long will a 100Ah battery run a fridge?
A 12 V compressor fridge drawing 50 W while running, on about half the time, averages 25 W — so a 100Ah LiFePO4 battery runs it for about 41 hours (40 h 58 min). A 100Ah lead-acid battery used to 50% gives about 24 hours. An RV absorption fridge on electric is a much bigger load — run it on propane off-grid.
How to work it out
- 100 Ah × 12.8 V × 80% usable = 1,024 Wh
- 50 W × 50% of the time = 25 W average
- 1,024 Wh ÷ 25 W = 41 hours (40 h 58 min)
These numbers follow Victron’s worked example of a 12 V fridge: a compressor of about 50 W (4.2 A) that runs half the time uses about 50 Ah a day. Your fridge’s real duty cycle depends on its insulation, the weather and how often the lid opens.
Adjust for your project
More options: DoD · Duty · Battery temp
- In hours and minutes
- 40 h 58 min
- Usable energy
- 1,024 Wh
- Average draw from the battery
- 25 W
- Battery current while running
- 3.9 A
- In days
- 1.7 days
Runtime at other loads
| Load | Runtime | Battery current while running |
|---|---|---|
| 25 | 81.9 hours | 2 A |
| 50 | 41 hours | 3.9 A |
| 100 | 20.5 hours | 7.8 A |
| 200 | 10.2 hours | 15.6 A |
| 500 | 4.1 hours | 39.1 A |
| 1000 | 2 hours | 78.1 A |
| 2000 | 1 hour | 156.3 A |
What changes how long the fridge runs
- Duty cycle is everything. At 25% duty the same fridge averages 12.5 W and runs about 82 hours; parked in the sun at 75% it is closer to 27 hours. A cheap inline DC meter tells you yours in a day.
- A household fridge on an inverter is a different load. A 120 V fridge drawing 150–400 W while running (Champion’s chart) plus inverter loss can drain a 100Ah battery in well under a day — see how many watts a refrigerator uses per day.
- Lead-acid needs to stay above half. Trojan recommends 20–50% discharge, so plan on 600 Wh from a 100Ah lead-acid battery — about 24 hours of this fridge.
- Freezers run harder. A 12 V fridge set as a freezer, or a chest freezer, runs a longer share of the time; set the duty higher under More options.
- RV absorption fridges are different. The propane/electric fridge in many RVs uses a heater on electric, not a compressor — Champion lists RV fridges at 150–600 running watts. Off-grid, run it on propane.
To keep it running indefinitely, the panels need to replace about 600 Wh a day — how many solar panels to charge a 100Ah battery does that sum. For the energy in the battery itself, see how many watt-hours in a 100Ah battery.
Different size? Use the full Battery Runtime Calculator.
What you’ll need
- 12 V compressor fridgePremium price
A compressor fridge runs straight off the battery with no inverter loss — usually the single biggest load in a van or boat system.
See options on Amazon (opens in a new tab) - Inline DC watt meterBudget price
Sits between a 12 V device and its supply and shows watts, amps and watt-hours used — handy for measuring a 12 V fridge, Starlink Mini or fan.
See options on Amazon (opens in a new tab) - 12 V 100 Ah LiFePO4 batteryPremium price
About 1.28 kWh rated in a box roughly the size of a group 24–31 lead-acid battery at around half the weight. Check the BMS discharge limit and whether it can charge below freezing.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How long will a 100Ah lead-acid (AGM) battery run a 12 V fridge?
About 24 hours at 50% depth of discharge (600 Wh usable).
How long will a 100Ah battery run a 12 V fridge that runs a quarter of the time?
About 81.9 hours (3.4 days) on a 100Ah LiFePO4 battery.
How long will a 100Ah battery run a 120 V fridge through an inverter?
About 14 hours for a fridge drawing 200 W a third of the time through a 90% inverter.
Other common sizes
- How long a 100Ah battery lasts with a 1000W inverter — 55 min at full load (12.8 V LiFePO4)
- How long a 200Ah battery lasts with a 2000W inverter — 55 min at full load (12.8 V LiFePO4)
- How long a 100Ah battery runs a CPAP — 15.4 hours at 60 W (LiFePO4, via inverter)
- How long a 100Ah battery lasts with a 200W load — 4.6 hours (LiFePO4, via inverter)
Sources
- Victron Energy — Lithium Battery Smart manual, technical data (opens in a new tab) — LiFePO4 12.8 V: cycle life 2,500 at 80% DoD, 3,000 at 70%, 5,000 at 50% (to 80% of capacity); 92% round-trip efficiency; 12.8 V 100 Ah: recommended continuous discharge ≤100 A (1C), maximum 200 A; capacity about 20% lower at 0 °C; charge only between +5 °C and +50 °C.
- Trojan Battery — Technical support FAQs (opens in a new tab) — “We generally recommend a discharge of 20 to 50% of the battery’s rated capacity even though the battery is capable of being cycled to 80%”; 20-hour and 100-hour ratings; freezing points by state of charge.
- Trojan Battery — 27TMX data sheet (opens in a new tab) — Group 27 flooded: 85 Ah (5-hr), 97 Ah (10-hr), 105 Ah (20-hr), 117 Ah (100-hr); state of charge vs open-circuit voltage table; charger settings.
- Victron Energy — Energy Unlimited (book) (opens in a new tab) — Lead-acid charge efficiency 80–95% (85% suggested as a starting value); battery energy efficiency about 75% for full cycles, about 89% in partial state of charge; inverter efficiencies above 90%.
- Champion Power Equipment — Generator Wattage Chart (opens in a new tab) — Typical running and starting watts for household, RV and job-site appliances (a manufacturer’s planning chart — your nameplate wins).