"State of Health" (SoH) is the figure that describes how much usable capacity an EV battery has left compared to when it was new, shown as a percentage. A battery at 100% SoH charges to its full original range; one at 85% SoH will only ever charge to about 85% of that original range, even at a "full" charge.
What counts as normal
| State of Health | What it means |
|---|---|
| 95%+ | Nearly new — negligible day-to-day difference |
| Mid-80s to low-90s | Typical for a healthy EV a few years old with normal use — this is what to expect on a decent used example |
| Around 80% | Noticeable range loss compared to new, but still normal for an older or higher-mileage car |
| Below 70% | Worth a professional evaluation — this is also roughly where most manufacturer warranties draw their guaranteed minimum |
As a rough guide, batteries typically retain around 85–90% of capacity after roughly 1,000 charge cycles, and 75–80% after roughly 2,000 cycles — though this varies by battery chemistry, climate, and how the car is charged and used. A single year of range loss over about 20% is the clearer warning sign of something faulty, rather than ordinary degradation.
What affects degradation
- Frequent DC rapid charging generates more heat and stress than slower AC/home charging — occasional rapid charging is fine, but a car that's almost never charged any other way may degrade a little faster.
- Consistently charging to 100% and leaving it there, or regularly running the battery down to empty, is harder on long-term health than keeping it in a more moderate range day-to-day (many manufacturers suggest roughly 20–80% for daily use, saving 100% charges for longer trips).
- Heat generally degrades batteries faster than cold — hence why hot climates tend to show more degradation than the UK's, though extreme cold temporarily reduces usable range too (a separate effect from permanent capacity loss).
- Age and mileage both matter — a low-mileage but older car and a younger high-mileage car can end up with similar SoH for different reasons.
How to check it
- The manufacturer's own app is the easiest starting point — many EVs surface a battery health or capacity figure directly to the owner's companion app.
- A Bluetooth OBD-II dongle with a model-specific app can read more detailed pack data than the dashboard shows, including individual cell information on some models.
- An independent EV diagnostic service or EV-experienced garage can connect directly to the battery management system and identify specific issues — worthwhile for a higher-value used purchase, or if something already looks off.
- Compare against a range baseline — if you know the car's original WLTP range, a car showing dramatically less than its expected real-world range (see our real-world range guide) for its age and mileage is worth investigating further.
Warranty cover
Most manufacturers now guarantee the battery for around 8 years and 100,000–150,000 miles, with a promise that it won't drop below roughly 70% of its original capacity within that period — if it does, that's normally a warranty claim, not something you pay for. Terms vary by manufacturer and sometimes by battery chemistry, so check the specific warranty document for any car you're seriously considering, especially a used one where you'll want to know exactly how much cover is left.
Degradation figures here are typical ranges from published data, not guarantees for any specific car — battery chemistry, climate, and usage pattern all change the picture. When in doubt on a used purchase, get an actual SoH reading rather than estimating from age and mileage alone.