Battery fear drives used-EV pricing more than the batteries themselves justify. Buyers imagine a cliff-edge failure and a five-figure replacement bill, so they either overpay for peace of mind or walk away from good cars. This calculator turns the fear into numbers: an estimate of state of health from age and mileage, what the warranty actually guarantees, and what that health is worth in dollars against a listing's asking price.

How EV batteries actually age

Modern EV batteries degrade far more gently than early fears suggested. Fleet data from Recurrent and the Geotab EV battery degradation study show most packs losing only about 1–2% of capacity a year, with the loss front-loaded — fastest in the first year or two, then flattening to a slow decline. The result is that a five- or six-year-old EV commonly still holds 90% or more of its original range, not the half-dead battery buyers picture.

Chemistry, climate, and charging habits

Three things move the number. Chemistry: LFP packs (common in standard-range Teslas and newer budget EVs) age more slowly and shrug off heat and fast charging better than the NMC packs in most long-range cars. Climate: sustained heat is the biggest accelerator of calendar aging, which is why a Phoenix car ages faster than a Seattle one. Charging: leaning heavily on DC fast chargers, especially in the heat, adds wear — occasional road-trip fast charging barely matters, but daily fast charging does.

What the warranty really guarantees

Battery warranty terms vary by manufacturer, model, model year, in-service date, jurisdiction, and transfer rules. The Warranty tab starts with an illustrative profile and counts down both time and mileage; confirm the actual limits and capacity threshold using the vehicle VIN and warranty booklet.

Turning state of health into a price

Because range is what buyers pay for, state of health shows up directly in resale value — industry data suggests a swing from roughly 95% to 82% SOH can move price by 12–18%. This tool assumes the asking price reflects a typical same-age example, then adjusts up or down for how the specific battery compares. It's a screening estimate, not an appraisal: before you buy, ask the seller for a battery health report or run a diagnostic scan, which reads the true state of health straight from the car.