Choosing a power bank: mAh, watts and taking it on a plane

mAh and watt-hours

Capacity is stated in milliamp-hours (mAh). That figure is about the battery cells inside, which run at about 3.6 to 3.7 volts. To charge your phone, the power bank converts that to 5 volts or more, and some energy is lost as heat along the way. That is why many power banks carry a lower "rated capacity" next to the cell capacity: what actually comes out of the USB port.

Watt-hours (Wh) are the energy itself. You work it out like this: mAh × volts ÷ 1000. A 10,000 mAh power bank at 3.7 volts is therefore 37 Wh, a 20,000 mAh one 74 Wh and a 25,000 mAh one 92.5 Wh. The Wh figure is often printed on the power bank too.

Watts and USB Power Delivery

How fast your phone charges depends on the power in watts and on the protocol. The usual protocol over USB-C is USB-IF's USB Power Delivery (PD). For fast charging an iPhone, Apple names a USB-C charger with PD; how many watts depends on the model, for example 20 watts or more for the iPhone Air and 17e and 40 watts or more for the iPhone 17, 17 Pro and 17 Pro Max. For Super Fast Charging on Galaxy phones, Samsung names PPS, part of USB PD. So check that the power bank lists PD, and for a Galaxy also PPS.

A stronger power bank does no harm: the phone asks for what it can take. In our catalogue Hama lists 20 W with PD for the Powerbank PD 10000 mAh, Xiaomi 22.5 W for the Power Bank 10000mAh and Anker 30 W for the power bank with built-in USB-C cable.

If a power bank has several ports, the stated power is often the total. Charge two devices at once and each port gets less. The specifications give the figure per port.

For a laptop

A laptop that charges over USB-C asks for more: check how many watts your laptop's charger has. For a 65-watt laptop, look for a power bank that gives at least that much per port. Sandberg lists 100 W for the Powerbank USB-C PD 100W 20000 and 130 W for the All-in1 Powerbank 20000 PD 130W; UGREEN lists 145 W in total for the Nexode Power Bank 20000mAh.

Mind the cable as well. According to USB-IF, 100 watts at 20 volts goes over a USB-C cable rated for 5 amps. An ordinary 3-amp cable stops at 60 watts (20 volts × 3 amps).

With a cable, wireless or MagSafe

A built-in cable means one less thing to carry. UGREEN lists it for the Nexode Power Bank 55W, Baseus for the PicoGo.

A MagSafe or Qi2 power bank snaps magnetically onto the back of the phone and charges wirelessly. Xtorm names the MagSafe system for the Magsafe Powerbank 10000 mAh; the 15 W in that name refers to the USB-C port. Apple makes its own MagSafe Battery, but Apple makes it for the iPhone Air. Wireless charging is handy on the go, but more energy is lost as heat than over a cable. With a case in between you need a MagSafe or Qi2 case.

Taking it on a plane

Under IATA's 2026 guidance for passengers travelling with lithium batteries, these rules apply to a power bank:

• A power bank always goes in your hand luggage, never in checked baggage.
• At most two power banks per person, each of at most 100 Wh.
• Above 100 Wh a power bank may not come along under that guidance, not even with the airline's approval.
• You may not recharge the power bank on board, and it should not power other devices during taxiing, take-off and landing.

A 20,000 or 25,000 mAh power bank stays under 100 Wh. Airlines may set stricter rules, for example on using a power bank on board: check your airline's site before you leave. Every model is under power banks, and separate cables under cables.