Amp-hours vs watt-hours
Amp-hours (Ah) describe charge; watt-hours (Wh) describe energy. Because batteries come in different voltages, watt-hours are the fair way to compare them. Multiply amp-hours by the nominal voltage to get watt-hours.
Wh = Ah × V
Ah = Wh ÷ V
Wh = mAh × V ÷ 1000
Examples
- 100 Ah LiFePO4 at 12.8 V = 1,280 Wh
- 20,000 mAh power bank at 3.7 V = 74 Wh
- 5 kWh wall battery at 51.2 V = 97.7 Ah
Airline battery limits (FAA)
| Battery size | Carry-on rule |
|---|---|
| Up to 100 Wh | Allowed in carry-on; no approval needed |
| 101–160 Wh | Airline approval required; limit of two spares |
| Over 160 Wh | Not allowed on passenger aircraft |
Spare lithium batteries and power banks must be in carry-on bags, never checked luggage.
Frequently asked questions
How many Wh is a 100Ah battery?
1,200 Wh at 12 V or 1,280 Wh for a 12.8 V LiFePO4 battery.
Can I take a 20,000 mAh power bank on a plane?
Yes. At 3.7 V it is about 74 Wh, under the 100 Wh limit.
Which voltage should I use for mAh?
Use the cell's nominal voltage, usually 3.6 or 3.7 V, not the 5 V USB output.