E-bike battery specs explained: volts, Ah and Wh
Read e-bike battery voltage, amp-hours and watt-hours, compare nominal energy and distinguish motor power, charger output, measured capacity and compatibility.
UpdatedDIY e-bike battery calculator: capacity planning
Updated
Estimate nominal watt-hours for a DIY or conversion project from your full trip distance, assumed energy use and reserve. This calculator plans capacity; it does not design a battery pack, check component compatibility or guarantee riding range. Use an approved battery matched to your exact system.
THE BATTERY WORKBENCH
How much battery do you need?
Set your trip distance and energy use. See the capacity, reserve and equivalent amp-hours together.
18.6 mi (30 km)Include the return journey if you cannot charge at your destination.
24.1 Wh/mi (15 Wh/km)Use your own measured consumption where available. The default is an editable example, not a tested bike rating.
The percentage of capacity you plan to leave unused.
YOUR CAPACITY ESTIMATE
Wh
Ah at V
450 Wh for the trip
Trip energy: WhRemaining area = reserve
This is the nominal capacity needed for your assumptions. Real range varies with hills, speed, load, weather, battery age and assistance.
THE MATH, OPENLY
18.6 mi (30 km) × 24.1 Wh/mi (15 Wh/km) ÷ 0.80 ≈ 562.5 Wh (calculated from unrounded inputs)
Put the result in perspective
Illustrative pack capacities compared with this estimate. This does not establish fit or compatibility with your bike.
400 WhBelow this estimate
500 WhBelow this estimate
625 WhMeets this estimate
750 WhMeets this estimate
1000 WhMeets this estimate
Default inputs are fictional planning assumptions, not a measured bike rating.
A planning link contains the trip distance, energy assumption, reserve, voltage and units. Share only values you want recipients to see. This calculator does not save trips or approve replacement batteries.
For planning only. Match replacement batteries to the bike manufacturer's approved voltage, mounting, connectors and battery management system. Capacity alone does not establish compatibility or safety.
How is battery capacity calculated?
Required Wh = distance in kilometres × energy use in Wh/km ÷ (1 − reserve/100). Amp-hours = watt-hours ÷ nominal voltage. Include the return journey when you cannot charge at your destination.
What do typical planning scenarios look like?
| Trip distance | Energy assumption | Required capacity |
|---|---|---|
| 12.4 mi (20 km) | 16.1 Wh/mi (10 Wh/km) | 250 Wh |
| 12.4 mi (20 km) | 24.1 Wh/mi (15 Wh/km) | 375 Wh |
| 12.4 mi (20 km) | 32.2 Wh/mi (20 Wh/km) | 500 Wh |
| 24.9 mi (40 km) | 16.1 Wh/mi (10 Wh/km) | 500 Wh |
| 24.9 mi (40 km) | 24.1 Wh/mi (15 Wh/km) | 750 Wh |
| 24.9 mi (40 km) | 32.2 Wh/mi (20 Wh/km) | 1000 Wh |
| 37.3 mi (60 km) | 16.1 Wh/mi (10 Wh/km) | 750 Wh |
| 37.3 mi (60 km) | 24.1 Wh/mi (15 Wh/km) | 1125 Wh |
| 37.3 mi (60 km) | 32.2 Wh/mi (20 Wh/km) | 1500 Wh |
How should you choose the assumptions?
Use measured consumption from your own bike and route where available. Hills, assistance, load, weather and stop-start riding change consumption. The default 24.1 Wh/mi (15 Wh/km) and 20% reserve are editable examples. A replacement battery must match the bike manufacturer’s electrical and mechanical requirements.
Plan a commute · Battery storage guidance · Estimate charging cost · All tools
Paired measurements are rounded for reading; calculations and planning links retain unrounded inputs. Fuel volume uses U.S. gallons. Original source sizing names and SI formula definitions retain their stated units.
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