Power banks

About 1.5–2.5 times for a 4,000–5,000 mAh phone, and a 20,000 mAh bank three to five times. Only about 60–70 % of the headline mAh reaches the phone: the cells are counted at 3.7 V, the port delivers 5 V or more, and the converter and cable lose 10–20 %. Test-Achats measured a 10,000 mAh bank charging a 5,000 mAh Galaxy S24 Ultra 1.22 times, not twice.

Under the ICAO Technical Instructions, which the FAA, EASA and IATA follow, a power bank travels in carry-on only: up to 100 Wh without approval, 101–160 Wh with the airline’s approval and at most two, nothing above 160 Wh. 20,000 mAh (74 Wh) and 27,000 mAh (about 100 Wh) pass; 30,000 mAh (111 Wh) needs approval; 43,000 mAh and up is over the ceiling. ICAO’s Addendum No. 1 to the 2025–2026 edition, applicable from 27 March 2026, adds: no more than two power banks per person, each protected against short circuit, none recharged on board. Airlines differ and may be stricter; the airline’s current rule applies.

On a growing number of airlines, no. Hong Kong’s Civil Aviation Department banned use on board from 7 April 2025, Korean carriers after the Air Busan fire of January 2025, Emirates from 1 October 2025, and Qantas, Jetstar and Virgin Australia from 15 December 2025. ICAO’s Technical Instructions addendum applicable from 27 March 2026 says a power bank must not be recharged on board and should not be used to charge a device, and IATA’s rules follow ICAO, so expect the rest to converge. Several airlines also want the bank in the seat pocket or under-seat bag, not the overhead bin. The airline’s current page is the rule.

The charge the 5 V port can deliver, printed beside the larger headline figure: “rated 12,000 mAh (5 V/3 A)” next to 20,000 mAh. It is smaller by arithmetic, since the same energy at 5 V is fewer mAh, plus 10–20 % converter loss. Compare banks on the figure measured the same way; a bank that prints both is being more open, not weaker.

20–30 W covers an iPhone and most Androids; 45 W with PPS is the ceiling for the fastest Samsung and Pixel phones; a tablet uses 30–45 W; a laptop needs 65 W or more. More watts than the device accepts change nothing, since the device sets the pace.

Usually because the phone kept running on the bank all night, with backups, syncing and the screen, on top of the 10–20 % conversion loss. It is the most common “my bank is broken” report, and in nearly every case the bank is fine. A bank that drains or fills in minutes is a different matter: that is a cell or battery-management fault, and the advice is to stop using it and claim the warranty.

Roughly the Wh divided by the input watts, times 1.3 for the taper at the end: 74 Wh at 18 W is about 5 h, at 45 W about 2 h. The input rating is only reached with a charger and cable that support it, and it drops sharply above about 80 %.

500–1,000 full charge cycles before the capacity drops noticeably, so several years of normal use. Cells age faster when kept at 100 % on a charger or stored hot; a bank left half charged in a drawer keeps best. Most warranties run 12–24 months and exclude normal wear.