How to choose a power bank
Rated capacity in mAh is not the energy you get. Cells sit at about 3.7V, USB delivers at 5V or higher, and the conversion plus heat costs roughly a third. A 10,000mAh bank realistically delivers around 6,000 to 7,000mAh to a phone. Watt hours is the honest unit, and it is the one airlines use.
Output wattage decides what it can charge
A phone wants 20W to 30W. A tablet wants 45W. A laptop wants 65W or more, and many thin and light machines want 100W. A bank with huge capacity and a 22.5W output will charge a laptop, very slowly, or refuse.
Check the per port figure, not the total
A bank advertised at 140W often means 140W shared. Plug in a second device and the first drops. If you charge two things at once, look for the split figures.
Recharge speed is half the experience
A 20,000mAh bank that recharges at 18W takes most of a day. The same capacity at 65W is usable overnight or over a lunch break. This spec is routinely buried.
Magnetic and wireless
Magnetic wireless banks are convenient and inefficient: expect roughly half the rated capacity to reach the phone, and expect heat. For maximum transferred energy, use the cable.
Airline rules
Most carriers allow up to 100Wh in the cabin without approval, and 100 to 160Wh with airline permission. Above that is refused. A bank that does not state its watt hours on the casing can be rejected at the gate.
Common mistakes
- Comparing two banks on mAh alone when they use different cell voltages.
- Buying a 25,000mAh bank for a phone, then carrying the weight every day.
- Assuming a built in cable is USB-C on both ends. Many are not.