How to choose a power bank for your phone

Choose the capacity for how many charges you need, the wattage your phone can accept, wireless only if your phone has a magnet ring or case, and check that the listing names the maker, the model and the Wh rating.

Published 30 October 2026 by ONDO.

Capacity: how many charges you need

Capacity is printed in mAh and should also be printed in Wh. As a rule of thumb, 60 to 70 % of the mAh reaches your phone. A 10,000 mAh power bank gives roughly one to two full charges of a modern phone, a 20,000 mAh one roughly two and a half to four and a half; the 20,000 mAh charges guide shows the arithmetic. Buy for the days you actually have: a commute needs less than a weekend away.

Wattage: how fast

Wattage tells you how fast the power bank can charge your phone, and how fast it can recharge itself. A higher figure only helps if your phone and your cable can accept it. Look for separate figures for the USB-C output, the wireless output and the input; a listing that gives only one number leaves you guessing.

Wireless or wired

Wireless magnetic charging is about convenience: the power bank stays on the phone and you keep using it. It needs a phone with a magnet ring or a magnetic case, it is slower than the cable, and it loses more energy. Wired charging works with every phone and is faster. A power bank that does both gives you the choice. The magnetic charging guide explains what the labels mean.

Size against capacity

More capacity means more cells, and more cells mean more weight and bulk. A magnetic power bank sits on the back of the phone, so its weight is in your hand all the time. If you mostly need a top-up during the day, a smaller one is more comfortable; if you need several charges away from a socket, accept the extra weight.

The airline limit

If you fly, stay at or under 100 Wh: about 27,000 mAh at 3.7 V. Above that you need airline approval, and some airlines do not accept it at all. See the power banks on planes guide.

What to check on a listing

• The Wh rating, as well as the mAh. Some airlines refuse power banks with no clear Wh rating.
• A real model number, and the manufacturer’s name and address; the EU Battery Regulation requires them on the battery label.
• Separate output figures for USB-C, USB-A and wireless, and the input figure.
• For wireless: whether the product is actually Qi2 certified, or only “magnetic”.
• Whether the seller publishes a declaration of conformity and safety test reports for that model.
• The seller’s name and address, the delivery time, and the returns and guarantee terms.
• Weight and dimensions, measured rather than estimated.

We hold the ONDO 20K to the same list, and the safety page shows where we stand on each document.