How long will a power bank last?
How long a power bank runs a heated gilet, a USB throw, a lantern or the Wi-Fi router, and how many times it charges a phone. Power banks are sold by milliamp-hours, so the answers here work for any brand of that size.
Every answer at a glance
Typical case. Click a figure for the low, medium and high settings and the worst and best case.
| Load | 10,000 mAh | 20,000 mAh | 26,800 mAh | 40,000 mAh |
|---|---|---|---|---|
| USB heated gilet | 3 h 42 min | 7 h 24 min | 9 h 55 min | 14 h 48 min |
| USB heated throw | 3 h 42 min | 7 h 24 min | 9 h 55 min | 14 h 48 min |
| Wi-Fi router | 2 h 30 min | 5 h | 6 h 42 min | 9 h 59 min |
| USB LED lantern | 9 h 15 min | 18 h 30 min | 24 h 47 min | 37 h |
| Phone (full charges) | 1.7 | 3.3 | 4.5 | 6.7 |
| Tablet (full charges) | 0.8 | 1.7 | 2.2 | 3.3 |
| Laptop over USB-C (full charges) | 0.5 | 0.9 | 1.2 | 1.8 |
How the sum works
A power bank's mAh figure is measured at the 3.7 V of its cells, so a 20,000 mAh bank holds about 74 Wh. Turning that into 5 V at the USB port loses heat, and independent tests of branded banks commonly find between two-thirds and nine-tenths of the rated energy comes out. This page uses 65% as the worst case, 75% as typical and 85% at best.
A phone or laptop loses another 10% or so charging its own battery, and a USB-to-12 V cable for a router loses about 10% more. Cold matters too: a bank left in a freezing car delivers noticeably less, so keep it indoors or in a pocket.
For the fridge, the heating or anything that plugs into a wall socket, a power bank is the wrong tool. That is what a power station is for, and the calculator covers those.
Sizes
- 10,000 mAh (about 37 Wh): Pocket size, the common free-gift bank.
- 20,000 mAh (about 74 Wh): The usual choice for a power cut: a couple of days of phone use.
- 26,800 mAh (about 99 Wh): About the largest you can take in hand luggage (under 100 Wh).
- 40,000 mAh (about 148 Wh): Brick-sized, and over the usual airline limit without approval.
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