Here is what makes buying a used electric or plug-in car genuinely different from buying a used gas car.
On a combustion car, the engine’s condition has to be inferred — from compression, oil condition, service history, the diagnostic memory, how it sounds. There is no single number.
On an EV or plug-in hybrid, the condition of the most expensive component in the vehicle exists as a number the car already knows. It is called State of Health, and the battery management system calculates it continuously.
So you are not really guessing. You are being not shown a readout that exists. That is a very different problem, and it has a solution.
First, the context that should lower your blood pressure
Before the warnings, the reassurance — because the fear around used EV batteries is largely out of proportion to the data.
Geotab’s 2026 study analysed telematics from more than 22,700 electric vehicles across 21 models, in fleets in the US, Canada and Europe. It found average degradation of 2.3% per year, which projects to roughly 81.6% of original capacity after eight years for high-use vehicles — and about 88% for low-use ones.
For scale, their 2020 study also found 2.3% and their 2023 study found 1.8%. Of the eleven models tracked from the 2023 data, eight have since stabilised at an average of 1.4% a year — degradation often slows after the first couple of years rather than accelerating. And researchers have not yet seen strong evidence of accelerated end-of-life collapse.
So the average used EV battery is in decent shape. The risk is not the average. The risk is the variance — and the only way to find out which side of it a particular car sits on is to read the number.
What State of Health actually is, and the four ways to get it
State of Health is the pack’s remaining usable capacity compared with when it was new. 88% SoH means roughly 88% of the original usable energy, which translates fairly directly into range.
Four routes to it, best first:
1. The manufacturer’s own diagnostic tool. The factory platform for the marque produces a full report. Insist on a complete PDF export with the VIN visible on it, not a photograph of a screen. Brands do not all calculate SoH identically, so a report from the car’s own system is the most authoritative version available.
2. An OBD-II scan by a shop that knows these cars. This gets you more than the headline number — cell-level voltages, charging history, thermal events. A caution: consumer apps can report nonsense if the battery size is configured wrongly for the specific model, which is a common source of alarming screenshots that mean nothing.
3. An independent battery certificate. Services including Geotab, Recurrent, Aviloo and DEKRA provide third-party SoH certification. Useful when buying remotely, and useful as a cross-check on a seller’s figure.
4. A real-world range check. On a long test drive, compare actual consumption and range against the car’s rated figures. It will not give you a precise percentage, but it will catch a wildly optimistic claim.
And the tactic to watch for: selective screenshots. A cropped image showing one favourable figure is not a battery report. Ask for the whole export.
How to read the number — with the caveat that matters
As rough guidance for a car a few years old, above roughly 90% is excellent, 85–90% is fine if the price reflects it, and below 80% on a car that has not covered huge mileage deserves a hard look or a walk.
But here is the caveat, and it is the thing most buying guides skip: one number without context is nearly useless.
SoH has to be read beside the car’s age, mileage, chemistry and the climate it lived in. A compact EV with air cooling and a premium sedan with a liquid-cooled pack are not comparable products, and the same percentage means different things on each. The right comparison is always against other cars of the same model and age, not against a universal threshold.
Which is exactly what makes the number worth getting rather than guessing at.
The three things State of Health will not tell you
This is where a proper inspection earns its money, because a single SoH figure can look fine on two cars that are heading in very different directions.
1. Cell imbalance. A pack is only as good as its weakest module. A voltage spread of more than roughly 80 to 100 millivolts between modules at a mid state of charge is a warning sign — it can indicate a weak cell group that will increasingly limit the whole pack regardless of what the overall capacity figure says. This does not appear in the headline number and it is visible on a proper scan.
2. Charging history — specifically the DC fast charging mix. Geotab found that vehicles using Level 3 DC fast chargers for more than 12% of their charging showed higher degradation, with the heaviest users reaching around 3.0% a year against the 2.3% average. Analysis elsewhere suggests packs that lived mostly on DC fast charging may age meaningfully faster than those charged at home.
Two cars can show the same SoH today — one that commuted on overnight home charging, one that lived on highway fast chargers — and diverge from here. The charging mix is in the logs.
3. How it was kept, not just how far it went. Geotab found degradation accelerates notably when a vehicle spends more than 80% of its time outside the commonly recommended 20–80% state of charge window. A car habitually left at 100% or run to near-empty has had a harder life than its odometer suggests. Also in the logs: repeated thermal limiting events.
And one more thing to establish in writing — whether the pack has ever been replaced, and if so whether the replacement was new, refurbished or salvaged. That is a documentation question, and a seller who cannot answer it is answering it.
Plug-in hybrids are the riskier purchase, and not for the reason you would guess
This is the most surprising thing in the research and it changes how you should shop.
An analysis of 1,000 plug-in hybrids by battery diagnostics firm Generational found average State of Health of 94.27%, against 94.94% for comparable EVs. Essentially the same.
But look at the spread. Standard deviation was 5.48% for PHEVs against 4.14% for EVs — and 4.7% of PHEVs came in below 85% SoH, against 1.5% of EVs. Roughly twice as likely to be a bad one.
The reason is usage. As Generational put it, PHEVs live more varied lives than EVs. Some owners plug in every night and drive the car almost entirely as a short-range electric vehicle. Others barely plug in at all and run it as a conventional hybrid.
Now here is the part that catches people out, and it is genuinely awkward. The PHEV used the way it is supposed to be used works its battery hardest. Daily charging and daily electric driving is the financially correct way to own one — and it cycles a small pack far more than occasional use does.
So on a used plug-in hybrid you have two condition questions that pull in opposite directions:
- The car that was diligently plugged in has a harder-worked battery and a gas engine that has done relatively little.
- The car that was never plugged in has an easier battery and an engine that did all the work — plus every short-trip problem that comes with it, including fuel dilution in the oil.
Neither is automatically better. But you cannot tell which one you are looking at from the mileage, and the answer is in the data. On a PHEV, check the battery and the engine’s condition, because the two tell you different halves of the story.
One genuine advantage to buying locally
Heat is the enemy of lithium packs, and this is where the Puget Sound region does well.
Geotab found that vehicles spending more than 35% of their time at 25°C degraded about 0.4 percentage points faster per year — and notably, the study did not cover cold climates at all, so the effect of our winters is less documented but is not the concern that heat is.
Our climate is mild and cool. A used EV that spent its life in Kirkland, Bellevue or Redmond has, on thermal grounds alone, had an easier time than the same car from Phoenix or Las Vegas. Combine that with the region’s relatively inexpensive, hydro-heavy electricity and local home charging looks good on the pack as well as the wallet.
Which makes where the car lived a question worth asking, and one that is answerable from the title history.
The warranty position, stated accurately
You will see “eight years or 100,000 miles” repeated as though it were a federal guarantee. It is not. There is no blanket federal traction-battery warranty applying to every EV.
What is true is that 8 years / 100,000 miles is the common manufacturer warranty on the traction battery, frequently with a capacity-retention threshold — often around 70% — below which a claim can be made. California and the states following its vehicle emission standards impose longer requirements on newer model years, and Washington follows California’s standards, so your specific car may have better coverage than the headline figure.
Two practical points. Check the warranty booklet for the actual car, by model year, rather than trusting a general number. And understand what the threshold means: a pack at 72% may be comfortably “within warranty” and still be a car you do not want. The warranty protects against failure, not against disappointment.
What a proper pre-purchase inspection on an electrified car covers
If you take one thing away: have the car inspected by someone who can read the battery, not only the bodywork. The checklist we would run:
- State of Health from the factory tool, complete export, VIN visible
- Cell voltage spread at a mid state of charge
- Charging history — the DC fast charge proportion, and the state-of-charge habits
- Thermal event log — repeated limiting, and when it occurred
- Stored and pending fault codes across the battery, charging and thermal management modules
- The 12-volt battery, which is still the most common reason an electrified car will not wake up at all
- Brakes — regenerative braking means the friction brakes are barely used, so in this climate expect corrosion rather than wear. It is normal to find most of the pad material intact and rotors that need replacing
- Tires, which wear faster under the weight and instant torque, and the suspension for the same reason
- Coolant loops — these cars have several, for battery, motor, power electronics and cabin
- The charge port and supplied cable, plus a confirmed successful AC and DC charge session
- On a plug-in hybrid, everything above plus a full combustion-engine inspection, including an oil condition and dilution check
Frequently asked questions
What is a good State of Health for a used EV?
As rough guidance for a car a few years old, above about 90% is excellent, 85–90% is fine if the price reflects it, and below 80% on a car without very high mileage warrants a hard look or a walk. But one number without context is nearly useless — SoH has to be read beside the car’s age, mileage, battery chemistry and the climate it lived in, and compared against other examples of the same model rather than a universal threshold.
How fast do EV batteries actually degrade?
Geotab’s 2026 study of more than 22,700 vehicles found an average of 2.3% a year, projecting to roughly 81.6% of original capacity after eight years for high-use cars and about 88% for low-use ones. Encouragingly, of eleven models tracked since their 2023 study, eight have stabilised at around 1.4% a year — degradation frequently slows after the early years rather than accelerating.
Does DC fast charging ruin the battery?
Not ruin, but it measurably matters. Geotab found vehicles using DC fast chargers for more than 12% of their charging degraded faster, with the heaviest users around 3.0% a year against the 2.3% average. The practical implication for buyers is that two cars showing identical State of Health today — one home-charged, one living on highway fast chargers — may diverge from here. The charging mix is recorded and a proper scan will show it.
Are used plug-in hybrids riskier than used EVs?
On battery condition, yes — about twice as likely to be a poor example. One analysis of 1,000 PHEVs found average State of Health almost identical to EVs (94.27% against 94.94%), but a wider spread, with 4.7% of PHEVs below 85% SoH versus 1.5% of EVs. The cause is that PHEVs live far more varied lives. And awkwardly, the PHEV used correctly — plugged in and driven electrically every day — works its small pack hardest, while the one that was rarely charged has an easier battery and a harder-worked engine.
Is the battery covered by warranty?
Usually by the manufacturer rather than by any federal rule — there is no blanket federal traction-battery warranty. Eight years or 100,000 miles is the common manufacturer term, often with a capacity-retention threshold around 70%. California and the states following its emission standards require more on newer model years, and Washington follows those standards, so check the warranty booklet for your specific car and model year. Note the threshold is usually well below what you would find acceptable: a pack at 72% can be within warranty and still be a car to avoid.
Does our climate help?
On thermal grounds, yes. Heat is the main accelerator of degradation — Geotab found cars spending more than 35% of their time at 25°C degraded about 0.4 percentage points faster each year, and the study did not cover cold climates. A used EV that spent its life around Kirkland, Bellevue or Redmond has had an easier thermal life than the equivalent car from Phoenix. Worth asking where the car lived.
Buying one? Let us read the battery first
Before you commit, have the pack read rather than described to you — State of Health from the factory tool, the cell voltage spread, the charging history and the thermal log, alongside a full inspection of everything that is not the battery. It costs a fraction of the difference between a good example and a poor one.
Eastside European Auto Service and Repair has been the Eastside’s dealer alternative since 2010, working on Mercedes-Benz, BMW, Audi, Volkswagen, Volvo, Porsche, Jaguar, Land Rover, MINI and Smart. ASE-certified technicians, over 75 years of combined experience, factory-level diagnostic equipment, and loaner cars available.
Call 425-823-8200 or book online. 12415 NE 124th St, Kirkland, WA 98034. Serving Kirkland, Bellevue, Bothell, Redmond, Issaquah, Mercer Island and Woodinville.