Quick answer: Pick a power bank by its watt-hour (Wh) rating, its output wattage and its charging standard, not by the mAh number alone. For flying, keep it in your carry-on and stay at or under 100Wh to avoid needing airline approval.
A power bank is one of the cheapest ways to stop a phone dying mid-day. But the big number on the box can mislead you, and airlines judge your battery by a different unit than the one printed on the front.
This guide covers sizing, output and ports, then the flight rules that apply to travelers in the US, UK, Canada, Australia and Europe. Airline rules change often, so always confirm with your carrier.
How big a power bank do I need?
Anker’s buying guide gives a rough sizing ladder:
- 5,000 to 10,000mAh suits commuting.
- 10,000 to 20,000mAh suits weekends or charging several devices.
- 20,000mAh and above suits long trips or laptops.
Expect to get less than the label promises. Anker says to plan on roughly 70 to 80 percent of the stated capacity being usable, because of conversion losses. A 10,000mAh bank typically delivers about 26 to 30Wh in real use, it adds.
What is the difference between mAh and Wh?
mAh measures charge. Wh measures energy, and it is what airlines use. The formula is Wh = mAh x volts / 1,000, per Belkin. For a typical 3.7V lithium pack, a 10,000mAh bank is about 37Wh, and 20,000mAh is 74Wh, as Anker and Practical Travel Gear both show.
If the label prints a Wh figure, use it. Practical Travel Gear says to use the voltage tied to the battery capacity, not the USB output voltage. If the label shows only mAh and no voltage, you cannot calculate Wh with confidence.
What output and ports should I look for?
- Wattage: Anker says phones need about 18W or more for proper fast charging. Tablets are generally served by 18 to 35W, and bigger tablets, consoles and light laptops need roughly 35 to 65W or more.
- Standard: USB-C Power Delivery is the most versatile for modern phones, tablets and many laptops. Fast charging only works if the bank, cable and device all support the same standard.
- Ports: USB-C handles input and output. USB-A helps with older gear. Wireless output is handy for top-ups but slower than a cable.
- Recharge speed: A smaller bank that refills quickly can be more practical than a big, slow one.
Phone battery wearing out? See our guide to checking phone battery health first. A tired phone battery drains power banks faster.
How do I choose a safe power bank?
Look for protection against overcharge, short circuits, overcurrent and overheating. Anker also advises looking for certification marks such as CE or UKCA, clear labelling and warranty information. It says reputable brands generally offer better cells and thermal management than ultra-cheap alternatives.
Stop using any bank that swells, gets very hot or is cracked. Belkin’s page says not to fly with a swollen, cracked or recalled power bank. If a phone is running hot while charging, our phone overheating fix guide can help.
Can I take a power bank on a plane?
Yes, in your carry-on only. TravelSentry says power banks count as spare lithium batteries and must stay in the cabin, even if your carry-on is gate-checked. Per Belkin’s summary of FAA limits:
| Rating | Carry-on | Airline approval |
|---|---|---|
| 100Wh or less | Yes | Not needed |
| 101 to 160Wh | Yes, max 2 | Required |
| Over 160Wh | No | Not allowed |
Airlines add their own limits. TravelSentry lists easyJet and Lufthansa at a maximum of two spares in the 100 to 160Wh range, and Ryanair at up to 20 spare batteries of 100Wh or less each. Belkin says Southwest allows 1 power bank of 100Wh or less from 20 April 2026, and that international flights under ICAO rules effective 27 March 2026 allow 2 per passenger with no recharging in flight. Belkin’s page is a manufacturer’s summary, not an official source, and it says rules change.
Several airlines also ban charging the bank from seat power and ask you to keep it out of the overhead bin, according to Practical Travel Gear. Delta, for example, does not allow a spare battery to charge a device during taxi, takeoff or landing.
What is a quick buying checklist?
- Pick capacity for your habits, then check the Wh rating.
- Match output watts to your biggest device.
- Confirm USB-C PD or the standard your phone uses.
- Check for safety protections and CE or UKCA marks.
- If you fly, stay at or under 100Wh and check your airline’s page.
More practical guides sit in our more mobile news and guides section.
Frequently asked questions
How many times will a 10,000mAh bank charge my phone?
It depends on the phone battery, but with 70 to 80 percent usable capacity, per Anker, expect fewer full charges than the label suggests.
Can I put a power bank in checked luggage?
No. Both TravelSentry and Belkin say power banks must go in carry-on bags only.
Does a higher wattage mean a bigger Wh rating?
No. Belkin notes that watt-hours measure stored energy, not charging speed, so a 140W rating does not change the Wh band.
Is a 20,000mAh power bank allowed on a plane?
At 3.7V it is about 74Wh, under the 100Wh line, per Practical Travel Gear. Check the label and your airline.