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Power bank real capacity
Why a 20,000 mAh power bank does not deliver 20,000 mAh to your phone, and how many charges you can really expect.
3.27
Charges for your device
74 Wh
Rated energy
62.9 Wh
Usable energy after conversion
12,580 mAh
Equivalent mAh at 5 V
17.33 Wh
Your device's battery
How it's calculated
- Rated mAh is counted at the cell's voltage (about 3.7 V). The pack must boost that to 5 V or more, losing energy as heat, so compare packs in Wh rather than mAh.
- Usable energy = rated Wh × converter efficiency. Charges = usable Wh × device charging efficiency ÷ the device battery in Wh.
- The efficiency defaults are typical assumptions. To measure a real pack, use a USB power meter and run it flat from full.
- Airlines limit lithium packs by watt-hours, not mAh. The rated Wh above is the figure to compare against those limits.