EcoFlow
DELTA 3
- Nominal capacity
- 1,024 Wh Manufacturer source for Nominal capacity (checked 2026-10-04; opens in a new tab)
When to consider another option Loads requiring 240 V or more than the continuous output rating.
Read the fit and limitationsCalculators Backup power planning
How long will my battery last?
Estimate runtime from simultaneous running watts or measured 24-hour energy, with a separate check against continuous output.
About 3 minutes You’ll need: battery capacity, running watts or measured daily energy, and reserve
Battery runtime calculator for household backup power planning
Saves on this devicePrivacy & options
Calculations run in this browser; inputs stay out of analytics. A draft saves here after your first change unless you turn saving off. You choose separately whether to save a result to My Household Plan or copy a permitted share link.
A measured-energy example
If the same appliances use 900 Wh of AC energy over 24 hours, that is an average energy load of 37.5 W. Their simultaneous running demand can still be 150 W or more; this illustrative running figure is checked against continuous output, while motor startup demand remains a separate question. The measured energy total describes use and does not have reserve or conversion losses applied in advance.
For an illustrative 1,000 Wh battery, a 20% reserve and 85% conversion-efficiency assumption leave 680 Wh of estimated usable AC energy. At 37.5 W average use, that gives about 18.1 hours (680 ÷ 37.5). These percentages are example assumptions, not ratings for a particular battery. Temperature, standby draw, changing use, and manufacturer limits can change the result.
DOE's storage overview explains energy versus power capacity and conversion losses; it does not prescribe the reserve or efficiency used in this example.
| Nameplate capacity | Illustrative usable AC energy (20% reserve, 85% efficiency) | At 37.5 W avg (900 Wh/24h) | At 75 W constant load | At 150 W constant load |
|---|---|---|---|---|
| 500 Wh class | 340 Wh | ~9.1 hours | ~4.5 hours | ~2.3 hours |
| 1,024 Wh class | 696 Wh | ~18.6 hours | ~9.3 hours | ~4.6 hours |
| 2,048 Wh class | 1,393 Wh | ~37.1 hours | ~18.6 hours | ~9.3 hours |
Check energy, target duration, power, and the real setup
Use either a constant running-load estimate or measured total AC energy for the selected devices over 24 hours. The system still needs enough continuous and surge power, safe placement, compatible charging, and a real test with the exact devices.
- Copy watt-hour capacity and continuous AC output from the exact system manual.
- Use a quick scenario only as a starting point. For measured mode, enter one 24-hour AC energy total for the same selected and custom loads; convert kWh to Wh by multiplying by 1,000.
- Choose a target outage window, compare simultaneous running watts with continuous output, verify startup demand separately, and perform a supervised discharge test before relying on the result.
Common questions
How do I calculate battery runtime from watt-hours?
Estimate usable AC energy as nameplate watt-hours × (1 − reserve as a decimal) × conversion efficiency as a decimal. Divide by constant running watts for hours of runtime. For measured-energy mode, divide usable energy by the measured 24-hour AC watt-hours divided by 24. These are planning estimates; continuous output and motor startup need separate checks.
What is the difference between watts and watt-hours?
Watts measure power at a moment. Watt-hours measure stored energy. A battery must have enough continuous and surge power for the devices and enough usable energy for the planned runtime.
Why is usable energy lower than the nameplate capacity?
The estimate holds back the reserve you choose and applies a conversion-efficiency assumption. Actual usable energy also varies by battery limits, inverter, temperature, age, settings, and load.
Will the calculator confirm that a refrigerator can start?
No. Motors and compressors can draw more power while starting than while running. Check the exact appliance demand and the battery system's surge rating, duration, and manufacturer limits; this remains unresolved even when you enter measured daily energy.
Can I use this to estimate what battery size I need?
Yes, as a planning estimate. Choose a constant running-load estimate or enter measured total AC energy for the same selected loads over 24 hours. The tool applies your reserve and conversion-efficiency assumptions once. Startup power, temperature, charging, and manufacturer limits still need separate verification.
Does a runtime estimate show whether refrigerated food is safe?
No. Battery runtime does not establish food temperature or safe storage time. Use the Food Safety Outage Calculator linked under Further reading for the separate refrigerator and freezer timeline question.
Plan first. Buy what is missing.
Compare 1 kWh LFP power stations for your runtime plan
After estimating your watt-hours and continuous watts, compare documented specifications and startup limits. These examples are not selected from your calculator answers.
BLUETTI
Elite 100 V2
- Nominal capacity
- 1,024 Wh Manufacturer source for Nominal capacity (checked 2026-10-22; opens in a new tab)
When to consider another option 240 V loads or a whole-home installation requirement.
Read the fit and limitations