The single most important number on an EV spec sheet is the battery size in kWh — kilowatt-hours. It sets the range, influences the price, and even affects how long charging takes. Yet it is widely misunderstood. This guide explains what a kWh actually measures, how it turns into range, and how much capacity an EV really loses as it ages.
What a kWh measures
A kilowatt-hour is a unit of energy — the amount used by a 1,000-watt appliance running for one hour. An EV battery's capacity in kWh is therefore the size of its "fuel tank." A 60 kWh pack stores 60 units of energy; a 100 kWh pack stores roughly two-thirds more. Bigger packs mean more range, but also more weight, more cost and longer full-charge times.
From kWh to range: the role of efficiency
Capacity alone does not determine range — efficiency does the other half. Efficiency is measured in kWh per 100 km: how much energy the car uses to travel that distance. The relationship is simple:
Range ≈ Battery capacity (kWh) ÷ Consumption (kWh/100 km) × 100
So a 75 kWh car using 15 kWh/100 km manages about 500 km, while a thirstier 75 kWh SUV using 22 kWh/100 km manages closer to 340 km. This is why a smaller, more efficient car can out-range a bigger, heavier one with the same battery — and why the kWh figure must always be read alongside the range cycle and efficiency.
Usable vs gross capacity
Manufacturers often quote two figures. Gross (or total) capacity is the full chemical capacity of the cells. Usable capacity is what you can actually access — the car keeps a hidden buffer at the top and bottom to protect the cells and extend their life. Usable is the number that matters for range, and it is typically a few percent smaller than gross. When two cars list different "battery sizes," check whether you are comparing gross with gross.
State of charge (SoC)
State of charge is simply how full the battery is, shown as a percentage — the EV equivalent of a fuel gauge. For most chemistries it is healthiest to keep daily charging in a roughly 20–80% window and only fill to 100% before a long trip. LFP batteries are an exception: they like a regular 100% charge, which also keeps their SoC reading accurate.
How much do EV batteries really degrade?
Degradation — the slow loss of capacity over years — worries new buyers most, and the reality is reassuring. Modern packs typically lose only a small percentage in the first year, then settle into a very gradual decline, often retaining around 85–90% of capacity after 150,000–200,000 km. Manufacturers back this with battery warranties (commonly 8 years) that guarantee a minimum remaining capacity. What accelerates degradation:
- Frequent DC fast charging versus gentle AC charging.
- Routinely sitting at 100% or near 0% for long periods.
- Sustained high heat.
Good thermal management — which nearly all modern EVs have — protects against the worst of these.
The bottom line
Read kWh as the tank size, efficiency as the fuel economy, and remember that usable capacity and the test cycle decide the real range. Degradation, once a genuine fear, is now slow and well-warrantied — a healthy EV battery should comfortably outlast the typical ownership period.
