Updated October 2026
Core conceptWhat Is EV Battery SOH? State of Health, Explained Simply
Every used EV shopper eventually runs into three letters: SOH. It stands for State of Health, and it's the single most important number in used EV shopping — more important than mileage, more honest than the dashboard range. Here's what it actually means.
SOH in one sentence
State of Health is the battery's current usable capacity, expressed as a percentage of what it held when new. A battery at 100% SOH holds everything it did on day one. At 90% SOH, it holds 90% — so a car rated for 300 miles new now goes roughly 270.
Think of it like a fuel tank that slowly shrinks. The car still works perfectly; the "tank" just holds a little less each year. That shrinkage is normal, predictable, and — crucially — measurable before you buy.
SOH vs. range vs. capacity: don't mix these up
Three related numbers get confused constantly:
- Capacity (kWh): how much energy the battery physically stores. A 75 kWh pack at 90% SOH effectively behaves like a 67.5 kWh pack.
- SOH (%): capacity now versus capacity new. The health score.
- Range (miles): what the dashboard guesses you'll go. This moves with temperature, speed, heater use, and driving style — it's an estimate, not a measurement.
The dashboard range lies to you a little every day. Cold morning? Range drops. Lead foot? Range drops. SOH doesn't care about any of that — it describes the cells themselves. That's why smart buyers shop by SOH, not by the number on the screen.
How SOH is actually measured
You can't see SOH on most dashboards. It's calculated by the car's Battery Management System (BMS) from voltage curves, charge throughput, and cell behavior — and read out through:
- OBD2 dongles with apps like LeafSpy (Nissan Leaf) or model-specific tools, which pull the BMS's own SOH figure.
- Battery reports from services like Recurrent, which estimate SOH from VIN-linked charging data and compare it against thousands of similar cars.
- Dealer battery printouts — some brands let dealers pull an official battery health report during service.
Each method has error bars. A BMS reading is the most direct; a Recurrent-style estimate is the most comparable across cars. For a full walkthrough, see How to Check a Used EV's Battery Health Before Buying.
What wears SOH down
Batteries don't degrade randomly. The same handful of factors show up in every large dataset:
- Heat. The big one. Batteries that live in hot climates degrade measurably faster — fleet data shows roughly 0.4% per year extra degradation in hot regions. This is also why older Nissan Leafs, which lack active liquid cooling, degrade faster than almost everything else.
- DC fast charging. Occasional fast charging is fine. Heavy reliance on it isn't: vehicles with a high share of fast charging (especially at high power) degrade roughly twice as fast as mostly slow-charged ones, per Geotab's 2026 analysis of 22,700 vehicles.
- Sitting at 100%. Keeping a battery pinned at full charge for long stretches accelerates wear. The effect is modest unless it's habitual (above ~80% of the time).
- Age and cycles. Even a pampered battery loses a little each year. Calendar aging is unavoidable — roughly 1–2% per year is simply the cost of time.
- Deep discharges. Regularly running to near-empty is harder on cells than shallow cycling.
Worth 5 minutes: a data-driven look at what physically wears EV batteries out — including a cut-open cell — backed by Geotab's 22,700-vehicle dataset.
What's a normal SOH?
| Situation | Typical SOH | Verdict |
|---|---|---|
| 2-year-old liquid-cooled EV | 94–97% | Normal |
| 5-year-old liquid-cooled EV | 88–93% | Normal — the healthy middle |
| 8-year-old liquid-cooled EV | 82–89% | Normal; check remaining warranty |
| Any age, 10+ points below peers | e.g. 78% at 4 years | Investigate or negotiate hard |
| Older Leaf in a hot climate | Can be 75–85% at 6–8 yrs | Known weak spot — price accordingly |
Context matters more than the raw number. 85% on an 8-year-old car in Texas is unremarkable. 85% on a 3-year-old car in Oregon means something went wrong — or the BMS needs recalibration, which occasionally happens and is worth ruling out before panicking.
The comparison that matters: never judge SOH in a vacuum. A Recurrent-style report compares the car against the same model, year, and region — that's the comparison that tells you whether this specific car is healthy or tired. See our Recurrent report walkthrough.
SOH and the warranty cliff
Most manufacturers warrant batteries against excessive degradation — typically guaranteeing at least 70% capacity for 8 years or 100,000 miles (the federal minimum, which transfers to used buyers). If a car's SOH is approaching that 70% line while still under warranty, that's not a disaster — it's a potential warranty claim. If it's at 71% with the warranty expired, that's just life. The warranty changes what every SOH number means, which is why buying out of warranty deserves its own decision process.
SOH myths that cost buyers money
"The dealer said the battery is fine." Without a number, "fine" means nothing. Ask for the SOH figure, the method used to get it, and the date. A verbal "fine" in 2026 is not diligence.
"Low miles means a healthy battery." Calendar aging doesn't care about the odometer. A 5-year-old EV with 20,000 garage-kept miles can have lower SOH than a 3-year-old with 60,000 highway miles but gentle charging. Miles matter less than heat and charging history.
"I can just look at the range estimate." The dashboard Guess-O-Meter moves with temperature and driving style. A car showing 250 miles on a 70°F day might show 190 on a 25°F day with the same battery. SOH is the stable truth underneath the moving estimate.
"All EVs degrade the same." The spread between a liquid-cooled Tesla and a passively-cooled older Leaf at the same age can be 10–15 SOH points. Model matters enormously — see degradation by model.
"A software update fixed the range, so the battery is fine." Updates sometimes recalibrate the estimate, not the chemistry. If an update "added" 15 miles overnight, the battery didn't heal — the guess got better. Check SOH before and after.
Frequently asked questions
Can SOH go back up?
Slightly, sometimes. BMS recalibration (a full charge/discharge cycle) can nudge a pessimistic reading upward by a point or two. Real chemical degradation never reverses. Anyone promising to "restore" SOH is selling something.
Is 80% SOH bad?
Not inherently. An 80% battery in a car priced like an 80% battery is a fair deal — it still drives fine, just shorter. 80% becomes a problem only when the price assumes 95%.
Does SOH affect charging speed?
Degraded batteries can charge slightly slower at the top end, but the bigger factor is the car's thermal management and the charger's power. SOH's main effect is range, not speed.
Do all EVs show SOH?
No. Tesla famously doesn't show a plain SOH figure (you infer it from rated range at 100%). LeafSpy exposes it on Leafs. Most others need an OBD2 tool, a dealer printout, or a third-party report.
Keep going: the complete used-EV battery health guide · degradation by model