In this guide
- kWh is how much energy the battery holds, like the size of a fuel tank
- The range on a spec sheet comes from a standard test, and real driving is usually different
- Speed, cold weather and heating all change real range
- Batteries lose capacity slowly over time, so for a used car ask about battery health
A spec sheet is full of numbers. Here are the ones that matter, and how to read them without being misled.
kWh and kW: two different things
kWh (kilowatt-hours) is how much energy the battery can hold. Think of it as the size of the fuel tank. kW (kilowatts) is how fast energy flows, for example how quickly a charger fills the battery. A bigger kWh number usually means more range, and a bigger kW number on a charger means faster charging.
The range on the spec sheet
Claimed range comes from a standard test done under set conditions. Different regions use different test cycles, so range figures from different cycles are not directly comparable. Treat the number as a way to compare cars tested the same way, not as a promise for your daily driving.
What changes real range
- Speed: motorway driving usually uses more energy than steady city driving.
- Temperature: cold weather typically reduces range, partly because of battery behaviour and partly because of heating.
- Heating and air conditioning: they draw energy from the same battery.
- Load, tyres and terrain: passengers, luggage, tyre choice and hills all play a part.
Total and usable capacity
Some listings quote the total battery size, others the usable part that the car actually lets you use. If you compare two cars, check you are comparing the same kind of number.
How batteries age
Over the years, a battery slowly holds a little less energy. How fast depends on the battery type, the climate, how the car is charged and how it is used. Frequent heat and very frequent fast charging can speed it up. The word for the remaining capacity is state of health.
Charging habits
Manufacturers give different advice on how full to charge the battery for daily use. Follow the guidance in the car's own manual rather than general rules from the internet.
What to do with this
- Plan with a safety buffer, not the full claimed range.
- For a used car, ask for a battery health report, and ask how it was measured.
- Check how the warranty treats capacity loss. The battery warranty guide explains what to look for.
General information
Every car is different. Confirm range and battery details for the exact car you are looking at.