Power banks and flight rules

You can take a power bank to Greece, but it travels in the cabin and only in the cabin. Lithium cells are barred from checked baggage on passenger aircraft, which makes the packing rule simple: nothing with a battery and nothing fragile goes in the hold. In practice that means the electronics all live in one carry-on and the checked bag holds clothes.

The number that governs whether you can bring a given bank at all is watt-hours, not milliamp hours, and it is usually printed in small type on the casing. The ordinary threshold is a hundred watt-hours: below it you can generally carry a bank without asking anyone, and above it you are into airline-approval territory with limits on how many. This is why large banks so often come in at ninety-nine point five watt-hours rather than a round number — they are built to sit just under the line.

Policies vary between carriers, so if yours is close to the threshold it is worth a look at the specific airline's dangerous-goods page rather than a general article.

If your milliamp-hour figure is all you have, the conversion is watt-hours equals amp-hours times volts, and the voltage to use is the cell voltage printed on the bank rather than the five volts its USB output suggests. A great many banks that read as enormous in milliamp hours turn out to be comfortably legal.

The seat outlet is a separate problem worth knowing about before you are in it. On a US carrier the outlet at the seat is a domestic three-pin socket, so on a nonstop from the States your chargers plug straight in at both ends of the journey with no adapter involved. The catch is mechanical rather than electrical: those sockets are frequently mounted vertically, and a heavy charger will slowly sag out of one under its own weight. A light low-wattage charger stays put where a big one will not, which is the actual reason to bring the small one rather than the powerful one. Most seats also carry a USB-A port alongside, which will trickle a phone at something like ten watts — fine overnight, useless for a laptop.

Charge the bank the night before you fly rather than the morning of. It is the one item in the kit that cannot be topped up quickly, and it is the one you will want intact when you land.