Battery capacity — from mAh on the label to the 100 Wh airline number
Airlines rate lithium batteries by watt-hours, not milliamp-hours. Wh = mAh × nominal voltage ÷ 1000. A 20,000 mAh power bank at 3.7 V cell voltage is 74 Wh — carry-on safe. A 30,000 mAh at 3.7 V is 111 Wh — over the 100 Wh limit and confiscated at security.
mAh is a charge measurement (milliampere-hours). Watt-hours are energy (charge × voltage). A battery's mAh label alone tells you nothing about how much stored energy it holds — you also need the voltage. Airlines regulate on energy (fire hazard scales with energy), so all lithium-battery rules are stated in watt-hours.
The exact factors
Wh = mAh × V / 1000 > Wh = Ah × V > 1 Wh = 3600 J = 3600 coulombs·V > Li-ion nominal voltage: 3.7 V (also 3.6, 3.65 for some chemistries) > LiFePO₄ nominal: 3.2 V > Charge in coulombs: Q = I × t; 1 Ah = 3600 C
Airline rules — the numbers
**IATA Dangerous Goods 2024 / FAA HMR §175.10:**
- ≤ 100 Wh: unlimited quantity in carry-on. No airline approval needed.
- 100–160 Wh: **carry-on only**, max 2 spare batteries, airline approval required.
- > 160 Wh: cargo only, hazmat declaration.
- **Spare (uninstalled) batteries: carry-on only, never checked baggage** — regardless of Wh.
The 100 Wh threshold covers essentially every phone, laptop, and mid-size power bank. The 100–160 Wh range covers professional camera batteries and some pro-tier power banks. Above 160 Wh is film/TV production equipment.
Common devices — actual Wh
| Device | Battery | Wh | Airline | |---|---|---|---| | iPhone 15 | 3349 mAh @ 3.87 V | 13.0 | Fine | | Galaxy S24 Ultra | 5000 mAh @ 3.87 V | 19.4 | Fine | | iPad Pro 12.9 | 10758 mAh @ 3.77 V | 40.6 | Fine | | MacBook Air M2 | 13.6 Ah @ 11.51 V | 156 | Approval, carry-on | | MacBook Pro 16 M3 | 8.9 Ah @ 11.5 V | 99.6 | Under 100 Wh, safe | | 10,000 mAh power bank | @ 3.7 V | 37.0 | Fine | | 20,000 mAh power bank | @ 3.7 V | 74.0 | Fine | | 27,000 mAh power bank | @ 3.7 V | 99.9 | Right at the line | | 30,000 mAh power bank | @ 3.7 V | 111 | Over — will be seized | | DJI Mavic 3 battery | 5000 mAh @ 15.4 V | 77 | Fine | | DJI Inspire 2 (TB50) | 4280 mAh @ 22.8 V | 97.58 | Fine, close |
**Note:** Apple prints watt-hours directly on the laptop battery underside. Anker and other power banks list Wh in fine print. Cheap AliExpress power banks often over-state mAh by 2–3× and quote it at cell voltage (3.7 V) while charging at output voltage (5 V) — real capacity is often half the label.
Worked example — power bank buying decision
You want maximum airline-safe capacity. Target 100 Wh, cell nominal 3.7 V:
Max mAh = 100 × 1000 / 3.7 = 27,027 mAh
Round down to 26,800 mAh (99.16 Wh). This is why 'Anker PowerCore 26800' is the largest widely-sold airline-safe capacity — the number is picked to sit just under 100 Wh at 3.7 V.
**The 27,000 mAh trap:** it computes to 99.9 Wh. TSA and airline staff often reject anything not clearly labelled ≤100 Wh, and some read the mAh number and reject anything ≥ 27,000. Anker prints '99.16 Wh' on the case for exactly this reason.
Why voltage matters — the 5V USB output confusion
USB-A outputs 5 V. A 20,000 mAh (cell) power bank does not deliver 20,000 mAh at 5 V. Energy is conserved: 74 Wh internally → ~66 Wh delivered (10–15% conversion loss). At 5 V, that is 13,200 mAh output. Manufacturers know this and quote the higher cell number; the label 'mAh' is at 3.7 V, always.
Wh, mAh, and phone charging math
iPhone 15 battery: 13 Wh. Fast charging at 20 W adds ~50% in 30 minutes = 6.5 Wh input × 15% loss = 5.5 Wh net = ~42% actual state of charge added. A 74 Wh (20,000 mAh) power bank has 74 × 0.85 (conversion) / 13 (phone battery) = 4.8 full recharges of an iPhone 15. Marketing routinely claims '5–7 charges' assuming 100% conversion, which is not physics.
Charge in coulombs — why battery engineers use Ah
1 Ah = 3600 C. Cell datasheets quote capacity in Ah at a stated discharge rate (0.2C, 1C, 2C). Higher discharge rates deliver less usable Ah — a 3 Ah cell at 0.2C might deliver only 2.5 Ah at 3C. Phone use is typically <0.5C so the rated capacity is close to real; drone motors at 15C+ see 20–30% capacity loss.
LiFePO₄ math is different
LiFePO₄ cells run 3.2 V nominal (vs 3.7 V for Li-ion). A '20,000 mAh LiFePO₄' pack is 64 Wh, not 74. Portable power stations (Bluetti, EcoFlow) using LiFePO₄ have lower Wh per mAh but far longer cycle life (~3,000 vs ~500). Airline rules are still by Wh, so a 100 Wh LiFePO₄ station is legal.
The five-second recap
Wh = mAh × V / 1000. Airline limit is 100 Wh carry-on, no checked luggage. Buy power banks labelled ≤ 99 Wh. A 26,800 mAh at 3.7 V is the practical max.
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FAQ
Where do I find the Wh number on a battery?+
Fine print on the case for power banks and laptop batteries. iPhone/Android phone batteries: multiply mAh (in Settings) by 3.87 V (typical) and divide by 1000. All under 25 Wh for phones — never a problem.
What voltage do I use if the battery doesn't list one?+
Standard Li-ion polymer: 3.7 V nominal. LiFePO₄: 3.2 V. Laptop packs: check the label (usually 10.8, 11.4, 11.5, or 15.4 V depending on cell count). Never assume 5 V (USB output) — that gives the wrong Wh.
Can I bring multiple power banks?+
Under 100 Wh: unlimited number in carry-on, no airline notification. 100–160 Wh: 2 spares max, with airline approval. Always carry-on; spare lithium batteries are prohibited in checked luggage worldwide since 2016.
Are these limits per battery or total?+
Per battery. Two 90 Wh power banks (180 Wh total) are legal because each is under 100 Wh individually. One 180 Wh unit is illegal without approval.
What happens if security seizes it?+
You surrender it at the checkpoint; it is destroyed. Airlines do not store or forward oversized lithium batteries. Some airports offer a mail-back service for a fee.
This article was written by The Turbo Unit Converter engineering desk (Electrochemistry & applied units) and last reviewed on 2026-07-10 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.