Spare lithium-ion batteries, including power banks, have to travel in the cabin rather than in checked baggage, with their terminals protected against short circuits. Regulators set the limits in watt hours rather than by physical size, airlines can add stricter caps of their own, and a swollen, damaged or recalled battery should not fly at all. Knowing those three things before you pack avoids most of the trouble at the gate.
Why lithium batteries get special treatment
Lithium-ion cells store a lot of energy in a small package, and they can overheat and enter a process called thermal runaway. According to the US Federal Aviation Administration, that can happen without warning if a battery is damaged, overheated, exposed to water, overcharged or badly packed, and it can also happen on its own because of a manufacturing defect: faa.gov
Cabin crew are trained to recognise and respond to battery fires in the passenger cabin, where they can reach a smoking bag. A battery fire in the cargo hold is far harder to fight. That is the practical reason spare batteries belong with you and not in a checked bag.
What the watt hour rating actually means
Energy content, not size, decides whether a battery is allowed on board. The FAA’s rules limit lithium metal batteries to 2 grams of lithium content each, and rechargeable lithium-ion batteries such as power banks to 100 watt hours (Wh) each. Larger lithium-ion batteries of 101 to 160 Wh are allowed with airline approval, with a limit of two of those spares per passenger. Anything above that range is not permitted in passenger baggage.
UK passenger guidance from the Civil Aviation Authority uses the same watt hour framing: batteries under 100 Wh are common in phones, laptops and cameras, batteries between 100 Wh and 160 Wh need airline approval, and batteries over 160 Wh cannot travel in passenger baggage at all: caa.co.uk
If the rating is not printed on the case, work it out. Voltage multiplied by amp hours gives watt hours, and for milliamp hours the sum is (V x mAh) / 1000. A power bank marked 3.7 V and 10,000 mAh therefore works out to 37 Wh.
Packing rules that apply almost everywhere
- Spare batteries and power banks go in carry-on baggage only. If a cabin bag is taken at the gate to be loaded into the hold, remove every spare battery and power bank first.
- Protect the terminals from short circuits: keep batteries in retail packaging, cover the ends with tape, use a case or pouch, or separate them so metal cannot bridge the contacts. Devices should be packed so they cannot switch on by accident.
- Phones, tablets and laptops are normally best kept with you. If one goes into a checked bag, it should be completely switched off and protected from damage.
- Damaged, recalled, overheating or swollen batteries should not be used and should never be carried on an aircraft.
- Check your airline’s own limits as well. The CAA’s passenger guidance allows two power banks per person and says a power bank should not be recharged on board. Some airlines apply tighter quantity limits, and you may be asked to keep power banks in your seat pocket instead of an overhead locker.
- Security officers can ask you to switch a device on, and their decision on what passes the checkpoint is final, as the US Transportation Security Administration states in its item guidance: tsa.gov
Why the rules differ between airlines and countries
Regulators publish a baseline, and airlines publish the version you actually have to follow. Two carriers flying the same route can set different caps on how many power banks a passenger may carry, and the baseline itself is revised from time to time. The reliable habit is to open the baggage or dangerous goods page of the airline you booked and treat its figure as your limit, rather than assuming that the most generous number you have read somewhere applies to your flight.
Bottom line: pack spares in the cabin, tape or pouch the terminals, know your watt hour number before you reach security, and check the airline’s own cap. It takes a few minutes at home and prevents a common reason for a bag being pulled at the gate.