How EV batteries degrade over time

Every lithium-ion battery loses a small amount of usable capacity every time it is charged and discharged, and even while it simply sits unused. This is normal chemical ageing, not a fault — the electrodes inside the cells undergo microscopic changes with every cycle, and that process is unavoidable in any lithium-ion battery, from a laptop to an EV.

The shape of a degradation curve

Degradation is not linear. Most EV batteries lose capacity fastest in the first year or two on the road, then the rate of loss slows and flattens out for many years afterwards. This is often called the "knee" shape of a degradation curve — a steeper initial drop followed by a long, gentle plateau.

This shape means a five-year-old EV with well-maintained charging habits can have a very similar SoH to a two-year-old one that has been treated harshly — age and mileage alone don't tell you which stage a specific car is actually in.

The four biggest factors

Where fast charging actually fits

Fast DC charging gets a lot of attention as a cause of degradation, and it does contribute — high charging currents generate more heat and stress inside the cells than a slow overnight AC charge. But for most drivers who use fast charging occasionally rather than as their only charging method, its contribution is smaller than commonly assumed; charge-to-100%-and-leave-it habits and hot climates tend to matter more over the life of the car.

What the largest fleet study to date found

Geotab's 2026 analysis of 22,700 electric vehicles across 21 models — the largest EV battery degradation study published to date — found an average annual degradation rate of 2.3%, and broke that average down by exactly the factors described above.

The same study found hot climates degrade batteries roughly 0.4 percentage points faster per year than mild climates, and that keeping a battery's state of charge in extreme ranges (above 80%) for long periods correlates with roughly 2.0% annual loss versus 1.4–1.5% for more moderate charging patterns — both consistent with the general guidance above.

Real-world SoH by age, at scale

A separate 2025 UK study by Generational analyzed more than 8,000 electric cars and vans across 36 brands, giving a clear picture of how SoH actually distributes by age in the used market.

The overall average across the full 8,000-vehicle sample was 95.15% — and even high-mileage vehicles (100,000+ miles) often maintained 88–95% SoH. The spread between the bottom and top 25% at each age is itself a useful data point: it confirms that individual charging and climate history genuinely matters more than age alone, exactly as the factors above would predict.