Power Bank Calculator
See roughly how many full charges a power bank gives your phone. The answer is an estimate, since real losses vary.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
A power bank's rating is at its cell voltage, and some of that energy is lost when it is converted for your phone. Multiply the bank's capacity by the efficiency to get the usable amount.
Divide that by the phone's battery size and round down, since a partial charge does not count as a full one.
Worked example
A 20,000 mAh power bank at 75% efficiency gives about 3 full charges to a 4,500 mAh phone.
Questions
Why is the count lower than the bank's number?
Conversion loss and the way the bank's voltage works both take a share. The efficiency figure covers that.
Does a fast charger change the count?
Mostly no. The stored energy is the same. Faster charging only shortens the time it takes to fill.
Can I count on this number?
Use it as a rough guide. Cables, the phone's use during charging and heat all change the real result.
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