Cycling & E-bike

E-bike battery Wh.

Battery capacity in watt-hours is volts times amp-hours. Convert a pack to Wh or back to Ah, estimate how long your charger takes, and see where the pack sits against the FAA air-travel limits. Runs in your browser.

Battery and charger

Battery voltage

Nominal voltage on the label: 36, 48 and 52 V are common.

Capacity

Amp-hours on the label. Leave blank to convert a Wh figure to Ah.

Or: Wh to convert to Ah

Charge from

Charge to

Charger output voltage

On the charger label, for example 42 V for a 36 V pack.

Charger output current

Charging efficiency

Losses in the charger and battery. 85 is a rule of thumb, not a published standard.

Watt-hours

Fill the form and press Calculate.

Worked example

A 36 V, 13 Ah pack is 36 × 13 = 468 Wh (0.468 kWh). A 500 Wh pack at 48 V is 500 / 48 = 10.4 Ah. A 42 V, 2 A charger delivers 84 W; at 85% efficiency 468 Wh takes 468 / (84 × 0.85) = 6.6 hours, and charging 20% to 80% (281 Wh) takes 3.9 hours. At 468 Wh the pack is above the 160 Wh maximum the FAA lists for spare lithium-ion batteries; check with the airline.

How it works

Wh = V × Ah. A watt is a joule per second, so watts multiplied by hours gives watt-hours. The voltage on an e-bike battery label is nominal, so the result is the rated energy. Ah = Wh ÷ V goes the other way.

Charge time = Wh to add ÷ (charger watts × efficiency). Charger watts are its output volts times output amps. The efficiency is yours to set; this is an average at a steady rate.

Air travel. The FAA says rechargeable lithium-ion batteries in carry-on are limited to 100 Wh each, and with airline approval a passenger may carry up to two spare larger batteries of 101 to 160 Wh. The page tells you which band your pack falls in; it does not say whether a given airline will accept an e-bike battery.

Sources and basis (opened 2026-10-08): US FAA PackSafe, Lithium Batteries (100 Wh limit; 101 to 160 Wh with airline approval, two spares); Wikipedia, Kilowatt-hour (energy is power multiplied by time; one kWh is 3.6 MJ).

FAQ

How do I convert volts and amp-hours to Wh?

Multiply them. A 36 V 13 Ah pack is 468 Wh; a 48 V 10.4 Ah pack is about 500 Wh.

How many amp-hours is a 500 Wh battery?

It depends on voltage: 10.4 Ah at 48 V, 13.9 Ah at 36 V. Always compare batteries in Wh, not Ah.

How long does an e-bike battery take to charge?

Wh to add divided by charger watts and efficiency. 468 Wh with a 42 V 2 A charger at 85% is about 6.6 hours from empty.

Can I take an e-bike battery on a plane?

The FAA limits spare rechargeable lithium-ion batteries to 100 Wh each, or 101 to 160 Wh with airline approval and two spares per person. A pack like the 468 Wh example is well above that, and airlines add their own rules, so check with the airline.

Why is the real charge time longer?

The estimate assumes a steady charge rate at the efficiency you enter. If your charger slows down near full charge, or the real efficiency is lower, the time is longer, so treat the figure as a rough minimum.

Disclaimer

Lithium-ion batteries can be hazardous if damaged or charged with the wrong charger. Use the charger made for your pack, follow the manufacturer’s instructions and check airline and carrier rules before travelling. This page gives arithmetic estimates only.