FOR-U PRACTICAL ANSWER
How Long Will a Home Battery Backup Really Last?
Last updated: August 22, 2026 • Method page by For-U.us
Short answer:
Runtime depends on two numbers: the battery energy you can actually use, measured in watt-hours (Wh), and the equipment load, measured in watts (W). A practical estimate is:
Runtime in hours = usable battery watt-hours ÷ average load in watts.
A 2,000 Wh battery with 85% usable energy provides about 1,700 Wh. At a steady 100 W load, the estimate is about 17 hours. At 500 W, it is about 3.4 hours.
Use the calculator
Estimated runtime: 17.0 hours
This is an energy estimate, not a guarantee. Real runtime changes with inverter efficiency, battery chemistry, temperature, startup surges, battery age, and how connected equipment cycles on and off.
Example runtimes from a 2,000 Wh battery
These examples use an 85% usable-energy allowance, giving 1,700 Wh available for the load.
| Average load | Estimated runtime | What this tells you |
|---|---|---|
| 10 W | 170 hours | Very small loads can run for days. |
| 50 W | 34 hours | Low-power essentials are realistic overnight loads. |
| 100 W | 17 hours | A modest continuous load approaches a full day. |
| 250 W | 6.8 hours | Runtime falls quickly as continuous demand rises. |
| 500 W | 3.4 hours | Heavy loads consume stored energy fast. |
The part people often miss
A device's label wattage is not always its average wattage. Refrigerators, pumps, air conditioners, and other motor-driven equipment can cycle and can demand a much larger burst of power when starting. That means two separate questions matter: Can the inverter handle the peak? and How much energy will the equipment use over time?
How to estimate your own home
- Write down the equipment that must stay on during an outage.
- Measure or estimate each item's average watts.
- Add the watts together to get the expected continuous load.
- Apply a conservative usable-energy percentage to the battery's rated watt-hours.
- Divide usable watt-hours by the average load.
- Leave extra margin for startup surges and unexpected loads.
Why For-U is testing this
For-U.us is developing a practical 24-hour household backup concept: keep the essentials alive first, then decide how much battery, inverter capacity, charging, and solar input are needed. This page is the calculation layer. As real-world measurements are added, the goal is to compare predicted runtime with observed runtime.
Related video
Grid Down: What Fails First Inside Your Home — a For-U preparedness video about what happens inside a home during a prolonged power outage.
Method and transparency
The examples on this page are calculations, not laboratory measurements. The formula is shown so the result can be checked independently. When For-U publishes a measured battery test, the battery model, rated capacity, connected loads, test conditions, elapsed time, and remaining charge should be listed so the result can be reproduced or challenged.