How to pick a power bank

A power bank is one of the cheapest ways to stop worrying about your phone dying. The numbers on the box can be misleading, though. Here is how to read them.

Capacity: what mAh actually means

Capacity is listed in milliamp-hours (mAh). A 10,000mAh bank sounds like it should charge a phone with a 5,000mAh battery twice, but in practice you get less. Some energy is lost as heat and in converting voltage, so expect roughly 60 to 70 percent of the rated capacity to reach your device.

As a rough guide:

• 5,000mAh: about one phone charge. Small enough for a pocket.
• 10,000mAh: one to two phone charges. The best size for most people.
• 20,000mAh: three or more phone charges, or a partial laptop charge. Heavier, better for travel.

Speed: look at the watts

Fast charging depends on wattage, and both the bank and your cable have to support it.

• 20W or more charges most phones quickly.
• 30 to 45W handles tablets and small laptops.
• 65W or more is what you want for charging a full-size laptop.

Check whether the listed wattage is per port or shared across ports. Many banks split their output when two devices are plugged in.

Ports

USB-C is the one to have. A bank with USB-C in and out can recharge itself from the same charger as your phone or laptop. A built-in cable is convenient, but it is also the first thing to wear out.

Flying with a power bank

In the US, power banks have to go in carry-on bags, not checked luggage. The usual limit is 100 watt-hours without airline approval, which covers almost every consumer power bank up to around 27,000mAh. Rules vary by airline and country, so check before you fly.

What to skip

Avoid unbranded banks with huge capacity claims at very low prices. Real battery cells cost money, and inflated mAh numbers are common. Stick to brands with a long review history.

See current power bank deals and USB-C charger deals.