EcoFlow Delta 2 running a 200 W fridge
1024 Wh × 0.95 usable ÷ (200 ÷ 0.90 + 8 W standby) ≈ 4.2 hours sustained.
Battery runtime calculator
How long will my battery last under load?
Enter your battery capacity in watt-hours, the running load, idle standby draw, usable depth-of-discharge, and inverter efficiency to estimate practical runtime for a Jackery, EcoFlow, Bluetti, APC UPS, or any custom 12 / 24 / 48 V bank.
Battery runtime calculator
Portable power and UPS runtime
Quick presets
Estimated runtime6 hr 11 min
Usable energy4.1K Wh
Total load670 W
Runtime days0.26 days
Energy per hour670 Wh
Battery draw670 W
Estimated runtime6 hr 11 min
How the math works
How the math works
- Usable energy (Wh) = Battery capacity × (Usable DoD ÷ 100). LiFePO4 packs published as 1 kWh typically deliver ~950 Wh usable; lead-acid only ~500 Wh.
- Inverter overhead = Load (W) ÷ Inverter efficiency. A 90% inverter consumes ~111 W to deliver 100 W AC.
- Runtime (hours) = Usable energy ÷ (Inverter-adjusted load + Standby draw).
Worked examples
Worked examples
APC Smart-UPS 1500 backing a 600 W server
865 Wh × 0.80 usable ÷ (600 ÷ 0.92) ≈ 1.1 hours — matches APC's published 65-minute spec.
DIY 48 V LiFePO4 5 kWh bank, 800 W load
5120 Wh × 0.90 ÷ (800 ÷ 0.92 + 20 W) ≈ 5.2 hours.
Battery runtime FAQ
Battery runtime FAQ
Why does my real runtime not match Wh × efficiency?
Manufacturers test at a steady mid-range load. Heavy loads (>50% C-rate) and very light loads (<5% C-rate) both shorten runtime because of voltage sag and inverter overhead.
What's the difference between Wh and Ah?
Wh = Ah × Volts. A 100 Ah, 12 V battery = 1200 Wh nominal. Always compare batteries in Wh to avoid voltage-class mistakes.
How long until LiFePO4 batteries lose capacity?
Quality LiFePO4 cells (EVE, CATL, BYD) hold 80% capacity at 3500–6000 cycles at 80% DoD — typically 10–15 years of daily use.
Can I run my fridge on a 500 Wh power station?
Modern Energy Star fridges average 100–150 W. Expect ~3 hours from a 500 Wh unit before inverter cutoff, or ~12 hours if the fridge cycles at 25% duty.
Does the calculator account for inverter standby?
Yes — set the standby field. Pure sine inverters typically idle at 8–25 W; large 3 kW inverters can idle at 30–50 W which dominates long-runtime estimates.
Backup Power Calculators
Battery & Generator Backup Calculators
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Add up critical loads (fridge, well pump, internet, a few lights), pick how many hours per day you need them, set a target number of backup days, and the calculator returns the battery bank size and how much solar recharge offsets the draw each day.
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List your running watts and the largest motor (well pump, AC compressor, fridge), apply LRA-based starting surge, and add a safety factor for fuel headroom and altitude derating.
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