For trips, festivals and sharing
A 20,000mAh power bank holds about twice an everyday one. It suits travelling, a festival weekend, long journeys, and charging two phones, or a phone and a tablet, from one battery. The price of that is weight and size: this is a power bank for a rucksack, a work bag or a glovebox rather than a jeans pocket. This page lists the power banks whose own name or description gives 20,000mAh.
What is here
Today the page holds a magnetic power bank with 22.5W fast charging. It clicks onto the back of the phone and charges it wirelessly, so you can keep using the phone while it charges, and it comes with a magnetic ring for phones and cases without magnets of their own. No cable is included, so use your own for its USB-C socket. It is also offered at 10,000mAh and 5,000mAh from the choices on its page, which are lighter on the back of a phone. The power bank with a built-in cable in 30,000mAh and over is offered at 20,000mAh too.
What 20,000mAh really gives
The mAh on the box is measured at the cells, at about 3.7 volts, and roughly two-thirds reaches the phone, the figure Anker uses in its worked example. So a 20,000mAh power bank gives about 13,400mAh to a phone: about three full charges of a phone with a 4,000mAh battery, or two phones charged and some left over. Charging wirelessly gives fewer, since wireless charging turns more of the power into heat. It holds about 74Wh.
Refilling a big power bank
This is the speed people forget. A 20,000mAh power bank holds about 74Wh, so on a 10-watt input it needs well over seven hours to fill; on a 30-watt USB Power Delivery input, closer to three. Fill it overnight before you go, from a wall charger with USB-C PD, and give it time to cool before packing. The guide to power banks explains input and output speeds.
Questions people ask about 20,000mAh power banks
Can I fly with a 20,000mAh power bank?
Power banks go in your hand luggage, never in a checked bag. The UK Civil Aviation Authority allows two per passenger, they must not be recharged on board, and each should be in a pouch or its packaging so its sockets cannot touch keys or coins. The limits are in watt-hours: under 100Wh is allowed in the cabin, 100Wh to 160Wh needs the airline's approval, and over 160Wh is not allowed in passenger baggage. At about 74Wh, a 20,000mAh power bank is inside the first limit. Read the watt-hours printed on your own, as cell voltages vary. Check your airline's own rules as well, as some are stricter.
Is a magnetic power bank this size heavy on the phone?
It is felt in the hand. For long calls or photos, many people take it off and use a cable instead, or choose the smaller version.
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