International, Ryanair and easyJet power-bank sources checked on 29 August 2026. A marketed mAh figure is not permission to fly; use the printed or manufacturer-specified Wh rating.
Quick answer
A 27,000mAh power bank can calculate to about 99.9Wh at a nominal 3.7V, but 27,000mAh does not guarantee 99.9Wh. Nominal voltage and actual capacity vary, and products marketed as “27K” may be 27,650mAh or another figure that crosses 100Wh. Read the printed Wh label and check the operating airline before you fly.
The near-100Wh boundary
| Label example | Calculation at 3.7V | Planning meaning |
|---|---|---|
| 27,000mAh | 99.9Wh | Near the ordinary 100Wh boundary; verify the printed Wh |
| 27,650mAh | About 102.3Wh | Above 100Wh at 3.7V; carrier policy becomes decisive |
| Printed 100Wh | No conversion needed | Use the printed rating and airline ceiling |
| Printed above 100Wh | No conversion needed | Do not assume approval; some carriers refuse it |
How the 99.9Wh estimate is calculated
When a label gives milliamp-hours and nominal voltage but no watt-hours, use:
Wh = mAh × V ÷ 1,000
For the familiar example, 27,000 × 3.7 ÷ 1,000 ≈ 99.9Wh. This is arithmetic, not certification. A different nominal voltage changes the result. The 5V or 9V USB output printed near a port may not be the battery’s nominal cell voltage, so do not substitute it when the label provides a dedicated battery rating.
Why “27K” is not a reliable clearance
Product names are marketing shorthand. A model sold as a 27K-class bank may list 27,000mAh, 27,650mAh or another capacity in its technical specification. At 3.7V, 27,650mAh is roughly 102.3Wh. Real devices above 100Wh therefore exist even when the product family sounds close to the boundary.
The printed or manufacturer-specified Wh rating is more authoritative than a generic web conversion. If the label is missing, unreadable or conflicts with the specification, do not round the answer down. Ask the manufacturer or operating airline, or choose a clearly marked device that stays comfortably inside the carrier’s published band.
Ryanair: 100Wh is a strict ceiling
Ryanair’s current rule does not provide a 100–160Wh approval route for power banks. Each bank must not exceed 100Wh under any circumstances, and a maximum of two may be carried. They must stay on your person or in the under-seat cabin bag, not in checked baggage or an overhead locker.
That means the distinction between 99.9Wh and 100.1Wh is operationally important. Use the exact printed rating rather than assuming every 27,000mAh bank sits below the line. A phrase such as “FAA approved” does not override Ryanair’s own ceiling and is not worldwide airline acceptance.
easyJet: do not treat the higher band as clean approval
easyJet’s main Dangerous Goods page currently says power banks not exceeding 160Wh are accepted, but an easyJet Holidays help page still states a 100Wh maximum. PrismGist therefore treats the 100–160Wh zone as confirmation-required rather than unconditional acceptance. If a 27K-class bank prints more than 100Wh, verify the current rule for your booking directly with easyJet before relying on the higher figure.
The wider 2026 baseline
ICAO’s specifications effective 27 March 2026 limit passengers to two power banks and prohibit recharging them during flight. IATA’s 2026 passenger guide gives ordinary planning guidance of no more than two power banks not exceeding 100Wh, cabin only, while warning that airlines may impose stricter conditions. The UK CAA also tells travellers to use Wh and check the airline’s rules.
- Carry power banks in cabin baggage, not checked luggage.
- Protect each bank against short circuit.
- Do not recharge the bank from aircraft power.
- Follow the carrier’s storage and device-charging restrictions.
- Remove the bank if a cabin bag is gate-checked.
- Do not carry a swollen, damaged, overheating or recalled unit.
Summary
At 3.7V, 27,000mAh is approximately 99.9Wh—but that result is not guaranteed by the product name. Check the printed Wh, exact capacity, nominal voltage, condition, quantity and operating airline. Ryanair refuses power banks above 100Wh; easyJet’s official pages still conflict above that boundary. Never turn a rounded “27K” label into automatic approval.
Official sources
- Ryanair: What items are permitted on board?
- easyJet: Dangerous Goods and power banks
- easyJet Holidays: lithium battery/power-bank help
- IATA 2026 passenger lithium-battery guidance
- UK CAA Pack Right guidance
Source check: 29 August 2026. Airline policy and the operating crew make the final decision.