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Quick answer
What does the Battery runtime calculate?
How long can a battery run a device at the entered power draw? This calculator uses battery capacity, average device power, and usable battery efficiency to estimate device runtime from battery capacity immediately in your browser.
With the values currently entered, the result is 5.7 hours — estimated runtime. It also shows usable energy, and energy lost.
How to use the Battery runtime
- Replace the example values with your own numbers.
- Review the result and supporting figures as they update automatically.
- Check the formula and assumptions before using the estimate for a decision.
Inputs used
- Battery capacity — entered in Wh
- Average device power — entered in W
- Usable battery efficiency — entered in %
Battery runtime formula
Battery watt-hours × usable efficiency ÷ device watts
Assumptions
- Average power draw stays constant.
- Battery age, temperature, and cutoff behavior are represented only by efficiency.
Practical guide
Battery runtime example and edge cases
How long can a battery run a device at the entered power draw? Let's use a concrete example, then look at the assumptions that can move the answer.
Example: A practical battery runtime scenario
For this example, use battery capacity of 80 Wh, average device power of 12 W, and usable battery efficiency of 85 %. These are starting values, so replace them with numbers that match your situation.
- Battery capacity
- 80 Wh
- Average device power
- 12 W
- Usable battery efficiency
- 85 %
Calculated result5.7 hoursestimated runtime
Start with estimated runtime. Then check usable energy, and energy lost to understand what sits behind the main result.
Example results use the default display profile. The calculator above follows your selected country and units.
How to read the result
- Read the main result first. The supporting figures for usable energy, and energy lost explain how the estimate is built.
- The method is Battery watt-hours × usable efficiency ÷ device watts. Keep the units consistent and use values from the same time period.
Edge cases worth checking
When battery capacity is unusual
Average power draw stays constant. Double-check this input before relying on the result.
When usable battery efficiency is uncertain
Battery age, temperature, and cutoff behavior are represented only by efficiency. Run a lower and higher value to see a useful range.
What changes the result most
Battery capacity
Change battery capacity on its own first. This shows how strongly it affects the answer.
Average device power
Change average device power on its own first. This shows how strongly it affects the answer.
Usable battery efficiency
Test a lower and higher usable battery efficiency. A small percentage change can move the final result more than expected.
Try a different scenario
Small changes show whether the answer is stable or sensitive.
Battery capacity: 10% lower
72 Wh5.1 hoursestimated runtime
Battery capacity: 10% higher
88 Wh6.2 hoursestimated runtime
Average device power: 10% higher
13 W5.2 hoursestimated runtime
Common mistakes
Check battery capacity
Average power draw stays constant. Make sure this matches the number you enter.
Keep usable battery efficiency consistent
Battery age, temperature, and cutoff behavior are represented only by efficiency. Use the same units and time period throughout the calculation.
Do not rely on one battery runtime scenario
Run a cautious case and an optimistic case. The range is often more useful than one exact-looking number.
Use this result well
How long can a battery run a device at the entered power draw?
Real speed, compression, battery health, and device overhead can change the result.