Power banks: how much capacity do you really need?

Power bank capacity is quoted in milliamp hours, and bigger sounds better. In practice, most people are carrying far more battery than they use.

Do the maths

A modern phone battery is around 4,500 to 5,000mAh. Power banks lose roughly 30% to voltage conversion, so a 10,000mAh bank gives you about one and a half full charges. A 20,000mAh bank gives you three to four.

When 10,000mAh is enough

Day trips, commuting, festivals. It fits in a pocket and weighs about 200 grams.

When you want 20,000mAh

Weekends away, long flights, or when you are also charging earbuds and a watch. It is also the largest size airlines allow in cabin bags without special approval (under 100Wh).

Output speed matters more than you think

A 22.5W or higher output with USB-C Power Delivery takes a phone to 50% in about 30 minutes. Older 10W banks take over an hour for the same charge.