Power Bank Charges Calculator
Estimate how much usable battery energy a power bank can deliver to your device.
iTechVora Tools
Power Bank Charges Calculator
Estimate full-charge equivalents using battery energy, not just mAh.
Free · No signup · Calculations run in your browser
Ready to calculate
How to use
Enter the advertised power bank cell capacity and device battery capacity. Start with the example 80% efficiency or use a value supported by your own measurements. Open Advanced to match the nominal voltages on your battery specifications.
Methodology
Energy (Wh) = capacity (mAh) × nominal voltage / 1,000. Full-charge equivalents = bank energy × overall efficiency / device battery energy. Efficiency is applied once, covering the total assumed loss from bank cells to energy stored in the device.
Worked example
A 20,000 mAh bank at 3.7 V stores 74 Wh nominally. At 80% efficiency it supplies 59.2 Wh of usable energy. A 5,000 mAh device battery at 3.85 V holds 19.25 Wh, giving about 3.08 full-charge equivalents.
Limits and sources
The sensitivity range varies efficiency by five percentage points either side of your input, capped at 1–100%. It is not a measured confidence interval. Battery health, temperature and running the device while charging affect outcomes. Do not enter a USB-output-rated mAh value with a cell voltage. See Anker’s explanation of usable power bank capacity.
FAQ
Why not divide the two mAh values?
mAh measures electric charge. Batteries at different voltages must first be compared using energy.
Is a partial recharge counted?
Results are full-charge equivalents: two 50-percentage-point recharges roughly equal one full charge under the same assumptions.
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Methodology version 1 · Updated September 28, 2026.