Why watt-hours matter
Air-travel battery rules are commonly expressed in watt-hours, while consumer power banks are often marketed in milliamp-hours. A reputable pack usually prints the Wh rating on its case; use that printed rating when available.
FAA guidance also treats power banks as spare lithium batteries, which means they belong in carry-on baggage rather than checked baggage.
The basic calculation
If a battery label gives nominal voltage and capacity in amp-hours:
Watt-hours = Volts × Amp-hours.
If capacity is shown in milliamp-hours, divide by 1,000 first.
Example: a cell pack labeled 20,000 mAh at a nominal 3.7V is 20 Ah × 3.7V = 74Wh.
Do not use USB output voltage for the calculation
A power bank may output 5V, 9V, 12V or higher through USB PD, but its energy rating is based on the battery pack’s stored energy. Use the nominal battery voltage and capacity printed by the manufacturer, or the manufacturer’s stated Wh figure.
Carry-on rules
FAA says spare lithium batteries and power banks are prohibited in checked baggage and must be carried in the cabin. Terminals should be protected against short circuits.
Larger batteries can require airline approval or may exceed passenger limits. The exact threshold and airline process must be checked before travel.
Check the airline as well as the regulator
International itineraries can involve different authorities and airline-specific restrictions. A blog post, including this one, should never be your final source for a regulated battery decision.
Before departure, open the current airline battery page and the relevant aviation-authority guidance.
Make the label readable
A worn or ambiguous battery label creates avoidable trouble at security or boarding. Keep the model and Wh rating visible and avoid traveling with damaged, swollen or recalled battery packs.
The simplest travel pack is one whose Wh rating is clearly printed and comfortably within current rules.
Current FAA thresholds
FAA passenger guidance updated in 2026 divides rechargeable lithium-ion batteries into three practical groups:
- 0–100Wh: generally allowed on passenger aircraft for personal use;
- 101–160Wh: requires air-carrier approval, with a limit of two spare batteries per person;
- above 160Wh: generally forbidden on passenger aircraft outside special categories such as certain mobility devices.
Power banks and portable chargers count as spare batteries, so they must remain in carry-on baggage.
Airlines may impose stricter limits, including quantity limits below the FAA maximum, so the airline’s own rule still needs to be checked.
Worked examples
10,000mAh at 3.7V
10,000mAh = 10Ah.
10Ah × 3.7V = 37Wh.
20,000mAh at 3.7V
20,000mAh = 20Ah.
20Ah × 3.7V = 74Wh.
27,000mAh at 3.7V
27,000mAh = 27Ah.
27Ah × 3.7V = 99.9Wh.
These examples show why two power banks with very different mAh marketing can still fall within the same 0–100Wh regulatory category.
Use the manufacturer’s printed Wh value when available because internal cell arrangements and nominal voltage conventions can vary.
Why the USB-C output number is not the battery voltage
A modern power bank might advertise 65W, 100W or 140W USB-C output and may negotiate 5V, 9V, 15V, 20V or other USB PD modes with connected devices.
Those output modes do not describe how much energy the battery stores.
The travel calculation uses battery energy: nominal battery voltage multiplied by capacity in amp-hours.
That is why a 20,000mAh power bank can be around 74Wh even though its USB-C port sometimes outputs 20V.
What to do if the Wh label is missing
First check the manufacturer product page and support documentation for the exact model.
If the product only lists mAh, look for the nominal battery voltage before calculating. Do not use the charger’s USB output voltage.
For air travel, a clearly printed Wh rating is preferable because it gives airline or security staff a direct value to inspect.
If the battery’s identity or rating is ambiguous, replacing it with a clearly labeled model can be simpler than arguing from your own calculation.
Gate-checked bags are the common trap
A power bank may be allowed in your carry-on but still become a problem if the airline later asks you to check that bag at the gate.
Remove power banks and other spare lithium batteries before the bag leaves your possession.
Keep them protected from short circuit and physical damage in the cabin.
Final pre-flight checklist
Before leaving for the airport:
- read the Wh marking on each power bank;
- confirm whether any unit exceeds 100Wh;
- obtain airline approval in advance if required for 101–160Wh batteries;
- keep power banks in carry-on baggage;
- protect exposed terminals;
- do not travel with a swollen, damaged or recalled battery;
- check the airline’s current battery page for route-specific or quantity limits.
Battery rules are safety rules, not just luggage preferences. Use the FAA and airline as the final authorities for the trip.