On a used electric car the battery is the car. Motor, brakes, suspension, bodywork — all cheaper to put right than the high-voltage pack, and the pack is the one part you cannot judge by looking at it. Sellers know this, which is why every listing says "battery is great" and almost none says what that means. The figure you actually want is state of health: how much of the pack's original capacity is still there.
An EV tells you far more about its battery than a gas car tells you about its engine — if you know which screens to open, which test to run, and which questions to ask. Here's the routine, from the driveway to the warranty booklet, and what a worn pack means for the years you'd own it.
State of health is not the range number
The range figure on the dash is an estimate built from the last stretch of driving. A gentle week in mild weather inflates it; a cold snap or a highway trip deflates it. Two cars with identical packs can show very different range numbers on the same morning, which is why owners call it the guess-o-meter.
State of health is the pack's usable capacity now, as a fraction of what it held new. It moves slowly, ignores yesterday's driving, and is the figure warranties are written around. Every pack degrades — most lose a little early and then settle into a slower decline — so you're not screening for degradation itself. You're screening for a pack that has lost more than its age and miles explain, and for the weak cell group an average hides: a percentage that lingers and then plunges near empty, or a car that cuts power earlier than it should.
Read the car's own battery screen
Some EVs display capacity directly — the Nissan Leaf's row of capacity bars beside the charge gauge is the best-known example, and a missing bar is the manufacturer's own admission. Others bury the number in a battery or energy menu, and a few keep a service screen that reports state of health outright. Owners' forums for the exact model tell you where it lives; walk in knowing.
Where the car won't say, the battery management system will. A cheap Bluetooth OBD-II adapter and a model-specific app — Leaf Spy for the Leaf is the well-known one, and equivalents exist for most mainstream EVs — read state of health and individual cell voltages straight from the pack in a few minutes. Ask before you visit whether you can plug in; the seller's answer to that is information either way. While you're there, photograph everything the screens offer:
- The state of health or capacity figure
- Cell voltage spread — a wide gap between strongest and weakest group is the weak group the average hides
- Lifetime energy delivered or charge-cycle count, where the car reports one
- DC fast-charge sessions versus Level 2 sessions, if the car keeps that tally
- The daily charge limit the owner has set — a car kept at 100% every night has lived harder
- Any battery warning, reduced-power message, or stored fault code
The 100%-charge range test
Ask the seller to charge the car to 100% the night before you come; many EVs default to a lower daily limit, and a single full charge is harmless. Note the displayed range at 100% and compare it with the official rating for that exact trim and model year when new. The ratio is a rough proxy for state of health — rough, because a car driven gently all week will flatter itself.
The better measurement is your own. Drive a loop you can repeat — mixed roads, normal climate control, no hypermiling and no racing — and note the battery percentage and the odometer at the start and end. Miles driven divided by the share of the pack used is the full-pack range under those conditions: forty miles that used 20 percent is roughly 200 miles from full. Heat, cold, and highway speed all cut range on a healthy pack, so a shortfall against the rating is a question, not a verdict. Fold the loop into the rest of your test drive and watch for the signs a weak pack shows on the move:
- The percentage falls unevenly — steady for a while, then a sudden step down
- Range drops faster than the percentage does, especially at highway speed
- A reduced-power or limited-performance warning appears well before the pack is empty
- Regenerative braking is weak when the pack is warm and not full
- The car cannot reach 100%, or reports a full charge at an oddly low range
Ask about the charging history
Lithium-ion chemistry ages with heat, time spent very full or very empty, and high current. DC fast charging is all three at once. It's a convenience, not a sin — a road-trip car that fast-charged a dozen times a year is fine — but a car that lived on fast chargers because the owner had no home charging, or ran rideshare, has typically worn harder than its odometer suggests. Hot climates age packs faster, and so does sitting full for weeks or near empty for months. None of this is fatal; all of it belongs in the price.
Then check the paper trail. Several EVs have had battery-related recalls, and a car that skipped its recall work may have a known defect still in the pack. Run the VIN through the NHTSA recall lookup, ask for dealer paperwork on any battery service or module replacement, and confirm the answers line up with what the screen told you.
- Where did you charge most — at home, at work, or at public fast chargers?
- What daily charge limit did you keep, and how often did you charge to 100%?
- Was the car ever left parked for long stretches full or nearly empty?
- Has the pack or any module been replaced, and is there paperwork?
- Has it had battery recall work done, and when?
- Has a software update ever changed the range or the charging speed?
Warranty transfer, in general terms
Most manufacturers warrant the high-voltage pack separately from the bumper-to-bumper coverage, for a term that runs years and carries a mileage cap, and many define a capacity floor — commonly quoted at around 70 percent — below which they will repair or replace. The exact term, the floor, and how capacity is measured vary by brand and model year and get revised, so read the warranty booklet for that specific car, not a forum summary. And note what the coverage is not: gradual loss above the floor is normal wear, and a pack a few points above it is entirely your problem.
The manufacturer's pack warranty generally follows the car to later owners, but confirm it. Extended or certified-pre-owned coverage often doesn't transfer; a salvage or rebuilt title commonly voids the battery warranty outright; and a pack opened by a non-dealer shop may have lost coverage on the spot. The cleanest check is a dealer's service department: give them the VIN and ask what battery coverage remains and whether it carries to you.
What a degraded pack costs to live with
No replacement price holds across brands, years, and shops, so this guide won't quote one. Out of warranty, a full pack is among the most expensive repairs on any car; module-level repair exists at some independent EV specialists, but not everywhere and not for every model. What you can price is the daily life of a smaller battery.
Range loss compounds. A pack at four-fifths of its original capacity in mild weather is far less than that on a January highway trip with the heat on, so trips that used to be one charge become two. You'll charge to 100% more often to compensate, which itself accelerates wear, and degraded packs often fast-charge more slowly, so the extra stops run longer. And the next buyer will run the same tests you just ran.
Treat the state-of-health number as a pricing input, not a pass or fail. A pack that has lost more than its age explains should take real money off what you offer, and a pack near the warranty floor with little coverage left is a car to walk away from unless the price already assumes a replacement. If you doubt your own reading, a pre-purchase inspection at a shop that works on EVs will put a number on paper.
Ignore the range number on the dash and go after state of health: the car's own battery screen or an OBD app first, a 100% charge and a repeatable driving loop second, the owner's charging history and the recall record third. Then read the warranty booklet for that car and confirm with a dealer, by VIN, what coverage carries to you. A pack that has aged in line with its miles is a fine used car at the right price; a pack that hasn't is the most expensive part of the car, quietly failing — the one thing a fresh detail and a full charge can't hide from a buyer who checks.