Battery Health (SOH) in a Used Imported EV: What to Check Beyond the Number on Paper

What SOH actually measures — and what it doesn't

State of Health is typically expressed as the battery's current usable capacity as a percentage of its original capacity when new. An SOH of 90% roughly means the pack can now store about 90% of the energy it could when it left the factory. What it usually does not tell you: how that capacity is distributed across individual cells or modules, how the pack performs under fast-charging load, whether any cells have been individually replaced or balanced, or how the reading was actually obtained.

Where the number comes from matters

• Manufacturer's own onboard estimate — convenient but often optimistic and inconsistently calculated across brands and software versions
• A dealer's diagnostic tool reading — better, but quality varies depending on the tool and how recently the battery was cycled
• An independent third-party test (for example a full charge-discharge cycle test from a specialist certifier) — the most reliable, because it measures actual delivered energy rather than reading an internal estimate

Beyond the headline percentage: what else to ask for

Request the battery's charging history if the seller or a diagnostic report can provide it. A pack that has spent its life on slow home AC charging generally ages more gracefully than one that has been fast-charged daily at a DC hub — both can still have identical SOH readings today, but their future degradation curves can differ. Also ask specifically whether any modules or cells have been replaced under warranty; a partial replacement can produce an SOH reading that looks healthy while masking an imbalance between old and new cells that shows up later as reduced usable range or erratic range estimates.

Mileage and age alone are unreliable proxies

Two EVs of the same age and mileage can have meaningfully different battery condition depending on climate exposure (batteries generally age faster in consistently hot climates), charging habits, and whether the car was ever left at a very low or very high state of charge for extended periods. This is precisely why importing from a colder northern European climate can sometimes work in your favor on battery longevity — but it is not a guarantee, and it should never replace an actual test.

Is a battery warranty enough protection without an independent test?

A remaining manufacturer battery warranty is valuable, but it typically only pays out once capacity drops below a defined threshold (commonly around 70%), not for the gradual loss between 100% and that floor. An independent test still matters for negotiating price and setting realistic expectations well before you'd ever need to make a warranty claim.

How much should a low SOH change the price I'm willing to pay?

There's no universal formula, but a pack noticeably below the typical degradation curve for its age and mileage should translate into a real price reduction, not just a verbal caveat — because replacement or a future capacity-related repair is a cost you may eventually bear, and it should be priced into the deal today.

SOH is a single data point on a curve you can't see. Test the car, don't just read the label.