The short version
- 10,000 mAh is the pocket-size sweet spot: about one and a half to two phone charges.
- Look for a USB-C port rated 20 W or more, otherwise charging crawls.
- Laptops need 45 to 65 W output and a 20,000 mAh pack.
Why you never get the number on the box
A 10,000 mAh power bank does not deliver 10,000 mAh to your phone. Converting voltage and shedding heat takes a share, so expect roughly two thirds of the printed figure. For most phones that works out to one and a half to two full charges.
A 20,000 mAh pack doubles that, but it weighs about as much as a thick paperback. If it stays in a bag, fine. If it lives in a pocket, the smaller size is the one you will actually carry.
Wattage decides the speed
Check the output of the USB-C port, not just the size of the pack. Around 20 W fast-charges most phones, while older 5 to 10 W ports take hours for the same job.
If the listing mentions Power Delivery (PD), the pack can agree the right speed with your device. That matters most for tablets and laptops, which simply refuse to charge from a weak port.
Flights, cables and other small print
Airlines generally allow power banks of up to 100 Wh — about 27,000 mAh — in carry-on bags only, never in checked luggage. Ordinary packs are well inside that limit.
Pass-through charging lets you plug the pack into the wall and the phone into the pack, so both are full by morning from a single socket. A magnetic wireless pad on your desk covers the rest of the day.
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