Calculating the capacity of an electric scooter battery: Wh, Ah, and volts

To determine the energy of an electric scooter battery, you multiply its nominal voltage in volts by its capacity in ampere-hours. The result is expressed in watt-hours (Wh). For example, a 72V battery with a capacity of 40Ah contains 72 × 40 = 2880 Wh. This figure, and not just the ampere-hours, allows you to compare two batteries with each other. Here's how to calculate it, how to verify it, and what it doesn't tell you.

Three units, three roles

• Volts (V) measure voltage, the "electrical pressure." On an electric scooter, it primarily determines the maximum speed the motor can reach.
• The ampere-hour (Ah) measures the amount of charge: a 40 Ah battery can theoretically provide 40 amps for one hour, or 20 amps for two hours.
• The watt-hour (Wh) measures energy: it's the product of the two. It determines the range, assuming equal consumption.

A common pitfall: comparing a 60V 40Ah battery to a 72V 32Ah battery by only looking at the ampere-hours. The first stores 2400 Wh, while the second stores 2304 Wh: they are almost equivalent in energy, even though the difference in Ah seems significant.

The step-by-step calculation

Let's take two batteries from our catalog. Our 72V 40Ah Performance battery for Dualtron Thunder and Thunder 2: 72 × 40 = 2880 Wh. Our 80V 40.5Ah Performance battery for Nami Burn-E: 80 × 40.5 = 3240 Wh. Both figures are listed on the product pages, and the calculation confirms them.

To convert to kilowatt-hours, we divide by 1,000: 2,880 Wh is equal to 2.88 kWh. This is the same unit used on an electricity bill.

Reading "20S10P": From cells to battery

A battery is an assembly of identical cells, often in the 21700 format. Its configuration is represented by two numbers:

• S (series): The number of cell groups connected in series. The voltages add up. With nominal 3.6V lithium-ion cells, 20S provides 72V, and 22S provides 79.2V.
• P (parallel): The number of cells in each group. The capacities are added together. Ten 5,000 mAh cells in parallel provide 50 Ah.

A 20S10P configuration of 5,000 mAh cells results in 72V x 50Ah = 3,600 Wh, for a total of 200 cells. The technical datasheet for a lithium cell provides the specifications for each individual cell.

Nominal voltage, full load voltage

The nominal voltage is an average value during discharge. A lithium-ion cell, when fully charged, reaches 4.2V. Therefore, a 20S battery will have a full voltage of 84V, even though it is often referred to as a "72V" battery. Some manufacturers specify 3.7V per cell instead of 3.6V, which slightly alters the advertised voltage for the same number of cells. This is why you sometimes see 18S batteries being sold as 67V. For comparison, the number of cells in series is always the most reliable indicator.

What watt-hours allow us to estimate

Battery life

Divide the usable energy by your measured consumption in Wh/km. The method and its pitfalls (speed, cold, weight) are detailed in our guide on the actual range of an electric scooter.

Charging time

Divide the amount of energy to be returned to the battery by the power provided by the charger. An 84V charger that delivers 5A provides approximately 420W: therefore, it takes more than six hours to return 2880Wh, and slightly more due to the slowing down of the charging process at the end. Our 4000W UltraChargeur can recharge a 2-3 kWh battery in about one hour, provided that the battery is designed for fast charging.

Weight and dimensions

With equivalent cell technology, energy capacity comes at a cost in terms of cells, which translates to weight and volume. A battery with a higher energy capacity must first fit within the deck, and this is often the primary limiting factor.

What watt-hours don't tell you

Two 2,880 Wh batteries can perform very differently at full acceleration. The current that a battery can provide depends on the type of cells, their number in parallel, the internal connections, and the BMS (Battery Management System). This is the difference between our standard batteries and our Performance batteries: the same voltage, sometimes even the same capacity, but not the same peak current. See our entire range of electric scooter batteries.