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The short answer
Airlines limit lithium batteries to 100Wh in carry-on, which is roughly 27000mAh at 3.7V, and they must be in your hand luggage, never checked. For most travellers 10000mAh is the sweet spot: two phone charges, pocketable, and well under every limit. Check the output wattage if you want to charge a laptop.
A power bank is a simple purchase made complicated by two numbers that are not what they seem: capacity, which you never receive in full, and output, which determines whether it charges your devices usefully or slowly.
Capacity: what you actually get
A 10000mAh power bank does not deliver 10000mAh to your phone. The cells are rated at 3.7V and your phone charges at 5V or higher, so there is a conversion, and conversion wastes energy as heat. Expect to receive roughly 60 to 70 percent of the rated capacity in practice.
So a 10000mAh bank delivers about 6500mAh of usable charge, which is one and a half to two full charges for a typical phone. A 20000mAh bank gives three to four. That is the realistic arithmetic to plan around.
Airline rules
- Under 100Wh: allowed in carry-on without approval. This covers everything up to about 27000mAh.
- 100 to 160Wh: usually allowed with airline approval, typically limited to two units.
- Over 160Wh: not permitted on passenger aircraft.
- Never in checked baggage, regardless of size. This rule is enforced consistently, and many airlines have added restrictions on using power banks during flight.
Look for the Wh figure printed on the unit. If only mAh is given, divide by 1000 and multiply by 3.7 for an approximate Wh value.
Several airlines now prohibit charging devices from a power bank during flight, and require power banks to be visible rather than in an overhead locker. Check your specific airline’s current policy before travelling, as these rules have been tightening.
Output: the number that decides usefulness
- 18 to 22.5W: fast charging for phones. Adequate for most travellers.
- 30 to 45W: charges tablets properly and will slowly charge many ultrabooks.
- 60 to 100W: genuine laptop charging. Necessary if the power bank is meant to keep a laptop alive.
Also check how the output is shared. A bank rated 45W total may deliver only 15W per port when two devices are connected. If you charge a phone and headphones together, that matters.
Power banks worth considering
Anker Nano 45W 10000mAh portable charger with built-in connector
The combination that suits most travel: 10000mAh keeps it well within airline limits and light enough to carry all day, while 45W output means it is not limited to phones. A built-in connector removes the cable you would otherwise forget, which matters more on a trip than it does at home.
Belkin 20000mAh 15W three-port power bank with cable included
Where one power bank serves a family or a group, capacity and port count matter more than peak output. Three or four full phone charges covers a day of travel for two people comfortably. The lower output means it charges phones at a sensible pace rather than at maximum speed.
TORRAS MiniMag 10000mAh magnetic power bank
Magnetic wireless charging is less efficient than a cable, so you get fewer charges from the same capacity. In exchange you get a phone you can hold and use while it charges, with no cable to catch on things. For sightseeing and navigation-heavy days, that trade is often worth it.
Miady 10000mAh slim portable charger, two-pack
The practical case for two smaller banks over one large one: you can leave one charging in the room while carrying the other, and a travelling pair can take one each. Capacity per unit is modest and the total is not, and both stay far below any airline threshold.
Belkin 10000mAh 15W three-port power bank
Port count in a pocketable size is the reason to choose this. Travel usually means several small devices rather than one large one, and charging them simultaneously overnight from one bank is more convenient than queuing them. Output is shared, so expect slower charging with everything connected.
What we liked
- Removes charger anxiety on long travel days
- Small models are well within airline limits
- Higher-output models can keep a laptop alive
- Cheap compared with being stranded without a phone
What we didn't
- You receive only 60 to 70 percent of rated capacity
- Large banks are heavy and airline-restricted
- Magnetic charging is less efficient
- Output is shared across ports
Practical travel notes
Charge it fully the night before
Power banks self-discharge slowly, and one packed months ago will not be full.
Keep it in hand luggage
Not negotiable. Lithium batteries are prohibited in checked bags on every major airline.
Take the right cable
A high-output bank with an old cable delivers slow charging. Use a cable rated for the wattage you bought.
Check the recharge time
A 20000mAh bank on a slow input can take eight hours to refill. Look for a bank that recharges at 30W or more if you need it ready overnight.
Avoid extreme heat
A power bank on a dashboard or in direct sun degrades quickly and, in the worst case, is a safety risk.
Retire swollen or damaged units
A power bank that has swelled, been dropped hard or gets hot in normal use should be disposed of at a battery recycling point rather than kept as a spare.
What size power bank can I take on a plane?
Up to 100Wh, roughly 27000mAh, without airline approval, and it must travel in your carry-on. Between 100 and 160Wh usually needs approval; above that is not permitted.
Why does my power bank not fully charge my phone twice?
Because voltage conversion loses energy. A 10000mAh bank typically delivers around 6500mAh usable, which is one and a half to two charges on most phones.
Can a power bank charge a laptop?
Only if it supports enough output, generally 60W or more for real use, and your laptop charges over USB-C. A 20W bank will slow the drain on a laptop rather than charge it.
Is magnetic wireless charging worth it?
It is convenient and less efficient, so you get fewer charges from the same capacity. For navigation-heavy days on foot it is often worth the trade, and for overnight top-ups a cable is better.
How long do power banks last?
Typically 300 to 500 full cycles before noticeable capacity loss, which for most people is several years. Heat shortens that considerably.
How to choose
Start at 10000mAh unless you have a specific reason to go bigger, since it covers two phone charges and fits in a pocket. Check the output matches what you want to charge, and check the per-port figure rather than the total. Keep it in your hand luggage, charge it the night before, and take a cable rated for the wattage you paid for.
