Battery Life and State of Health (SoH) When Buying a Used Electric Car

Used electric vehicles are becoming an increasingly common sight in the second-hand market. When evaluating one, a criterion emerges that has no equivalent in combustion cars: battery condition. How much range is left, how "tired" the battery has become, and how it will perform in the years ahead — all of this is captured in a single figure: State of Health (SoH).

Why Do Batteries Lose Capacity Over Time?

Lithium-ion batteries undergo chemical changes with every charge-discharge cycle. This process is unavoidable, but several factors determine how fast it happens:

DC fast charging: High current heats the battery cells and accelerates electrolyte degradation. Occasional fast charging is fine, but frequent daily use speeds up ageing noticeably.

Extreme state-of-charge levels: Regularly charging to 100% or running the battery close to 0% increases chemical stress. Most manufacturers recommend avoiding extreme charge levels in everyday use; check your car manual for its guidance.

Temperature extremes: Both intense heat and severe cold degrade battery chemistry. Older models with passive air cooling are particularly vulnerable in hot climates.

Calendar ageing: Batteries lose capacity even when sitting idle. A low-mileage car that spent years parked may surprise you with a lower-than-expected SoH.

What Is State of Health (SoH)?

SoH is the ratio of the battery's current usable capacity to its original factory capacity. An SoH of 100% means the battery performs identically to a brand-new one. An SoH of 80% means the battery has permanently lost 20% of its original capacity.

Take a car with a 60 kWh battery at 80% SoH: it effectively has 48 kWh available. That is a noticeable loss of range per charge. Battery warranties are typically tied to a specific SoH threshold, so learning the warranty terms and that threshold is critical when buying a used EV.

Why SoH Matters More Than Mileage

In a petrol or diesel car, mileage is a reliable proxy for wear. In an electric car, the picture is far more nuanced.

As a purely hypothetical illustration, a city commuter that charges nightly on AC at 80% and never sees a fast charger could show 88% SoH at 150,000 km. Meanwhile, a car used primarily for long motorway trips with frequent DC fast charging might be down to 76% SoH at just 70,000 km.

The takeaway: mileage alone does not tell you how healthy the battery is. Charging habits, climate exposure, and storage conditions influence SoH as much as — or more than — the odometer reading.

What to Check Before You Buy

1. Read the SoH value: Most modern EVs can display battery SoH through the infotainment menu or via an OBD-II adapter. Leaf Spy works for the Nissan Leaf; Tesla shows battery statistics natively in the car.

2. Run a range test: Charge the car fully (or to 80% and scale up), then compare the estimated range shown against the factory figure. A large gap is a warning sign.

3. Review the charging history: Many modern EVs log charging sessions. A pattern of frequent DC fast charging is a red flag.

4. Check the thermal management system: Models without active thermal management (TMS) degrade far more quickly in hot climates. Research whether the specific model you are looking at has active cooling before you visit.

5. Clarify warranty status: Many manufacturers offer a time- and mileage-limited battery warranty; coverage and the SoH threshold vary by manufacturer. Confirm whether the warranty transfers to a new owner and how much time remains.

Conclusion

A used electric car, approached with the right information, can be an excellent choice: fewer moving parts, lower maintenance costs, and a maturing technology. But overlooking battery condition can turn an apparently cheap deal into an expensive mistake. Before you visit the car, research the model's known battery issues by year — a CarExp report gives you exactly this pre-filter.

Get your CarExp vehicle report →

#ElectricCar #UsedEV #BatteryHealth #StateOfHealth #EVBuying