How to Really Check a Used EV's Battery Health (What a Tesla's Unknown Past Taught Us)

An EV With an Unknown Past, and a Battery That Held Up

A few weeks ago a story made the rounds on specialist sites: an American couple bought a Tesla Model 3 with an LFP battery, four years old and nearly 125,000 km (78,000 miles) on the clock, with zero information about how it had been charged before. An independent test came back with a state of health, the famous SoH, of 92 percent. In plain terms, the battery still held 92 percent of its original capacity, a genuinely reassuring number for a car with that mileage and no paper trail.

It is one specific case, but it captures the real problem facing anyone shopping for a used EV today: mileage alone tells you almost nothing about battery condition. Two identical Model 3s with the same odometer reading can have very different battery health, depending on how they were charged, where they sat in summer heat, and how often they were fast-charged. That is why checking SoH before signing over a used EV should be as routine as checking the service book.

What SoH Actually Means (It Is Not the Range You See)

SoH, state of health, is the percentage of capacity a battery still holds compared with when it was new. Do not confuse it with the charge percentage shown on the dashboard, which just tells you how much energy is in the pack right now, or with the manufacturer's claimed range under ideal conditions. A battery at 90 percent SoH or above is considered excellent, close to new. Between 85 and 90 percent is good, with a noticeable but acceptable drop in range. Below 85 percent, experts recommend a closer look, or negotiating a discount proportional to the remaining degradation.

Degradation is not linear: capacity loss is steepest in the first years and tends to flatten out afterward, which is exactly why two recent real-world cases involving the same model tell such different stories.

Two Real Cases, Side by Side: From 92 Percent to 79 Percent

Beyond the Model 3 with the unknown past, another test published in February 2026 tracked a 2019 Tesla Model 3 Performance owned by YouTuber Bjorn Nyland over several years: after roughly two years and 80,000 km, degradation stood at 8 percent, meaning 92 percent SoH, right in line with the case above. But by seven years and 182,000 km, capacity loss had climbed to 20.8 percent, with usable capacity down to about 58 kWh. The car still delivered a summer range close to 400 km, but the numbers confirm that past roughly 150,000 to 180,000 km the degradation curve tends to steepen, especially for cars with heavy fast-charging use or a history in harsh climates.

The practical takeaway: there is no universally safe mileage cutoff. Every car needs its own direct measurement.

How to Check SoH Before You Buy

There are three concrete ways to do it, in ascending order of reliability.

On-screen readouts or the manufacturer's app. Many EVs surface SoH, or an equivalent figure, in a diagnostics menu: Tesla shows it on the central touchscreen, Renault Zoe through its diagnostic menu, Hyundai and Kia through the Bluelink and UVO apps. It is the fastest method, but not sufficient on its own, since some displays lean optimistic.

Dedicated EV OBD scanners. Tools like OBDeleven, or brand-specific apps such as TeslaFi for Tesla or LeafSpy for the Nissan Leaf, read real data straight from the battery management system. They are inexpensive and something a trusted independent mechanic can run, not just the dealer.

An official certificate or independent report. Several brands, including Tesla, Volkswagen ID., Mercedes EQ, BMW, and the Hyundai-Kia group, let owners request an official SoH certificate at an authorized service center, usually for a modest fee. Alternatively, an independent report from a third-party technician using OBD data carries the same evidentiary weight and can be attached directly to the listing, making the negotiation more transparent for both sides.

Anyone selling a used EV should consider attaching one of these reports to the listing itself: it shortens the sale and removes a layer of buyer distrust from the start.

Battery Warranties: What the 70-80 Percent Threshold Really Covers

Most manufacturers offer a dedicated battery warranty, typically eight years or around 160,000 km, which kicks in once degradation crosses a conventional threshold, often set between 70 and 80 percent remaining SoH. In practice, wear of up to 30 percent of original capacity is treated as normal and does not entitle the owner to a free replacement within the warranty period.

It is worth separating this commercial warranty from Italy's statutory conformity guarantee for consumers, which runs 24 months, reducible to 12 for used vehicles if agreed in writing: that guarantee covers conformity defects, not ordinary cell aging. Buy a used EV outside the manufacturer's battery warranty window and you are effectively taking on the risk of further degradation yourself, which is exactly why an independent SoH check before purchase, not after, matters so much.

The 2027 Battery Passport Will Change the Rules

Starting February 18, 2027, the EU-wide Battery Passport requirement takes effect under Regulation (EU) 2023/1542. It will apply to all electric-vehicle batteries, batteries for light means of transport, and industrial batteries above 2 kWh placed on the European market. Accessible via a QR code, the digital document will carry data on composition, carbon footprint, recycled content, performance, state of health, repairability, and end-of-life handling.

For the used market, this is a real shift. Today, a battery's history depends on the seller's honesty or willingness to run an independent test, exactly the situation in the unknown-past Model 3 case. With the Battery Passport, part of that history becomes verifiable with a scan, cutting the uncertainty for anyone buying a secondhand EV, though how well it actually gets adopted at repair shops and in private listings in its first months will still need to be seen.

The Pre-Purchase Checklist

Always ask for SoH, not just mileage: two identical cars can carry very different battery health. Prefer an independent test or an official certificate over a seller's word alone. Treat SoH above 90 percent as excellent, 85 to 90 percent as acceptable, and anything below 85 percent as grounds for a discount or a closer look. Check whether the battery is still covered by the manufacturer's dedicated warranty, usually tied to a 70-80 percent SoH threshold within eight years or roughly 160,000 km. And from early 2027 onward, get used to reading the Battery Passport the way you read a service book today: another tool, not a replacement for a direct check, but one more layer of transparency for a used-EV market that badly needs it.