How to Correctly Read Battery Health When Buying a Used EV

Electric Vehicle Ownership
Author: Deniz Erkan
Creation: 22 October 2026

In a second-hand electric vehicle, the mileage alone tells you nothing; the real story lies hidden in the battery's SOH value.

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When buying a used electric vehicle, checking battery health should be as fundamental a habit as checking the mileage on a gasoline car - but mileage alone is not enough. Battery health, or SOH (State of Health), shows what percentage of the battery's original capacity is still usable. If a 65 kWh battery has dropped to 60 kWh, the SOH is approximately 92%. Knowing how to read this number correctly from the right report prevents you both from buying the wrong car and from paying more than the price you deserve.

Highlights

Battery capacity typically loses 2-3% per year; data from more than 22,000 vehicles shows an average annual degradation of 2.3%
Most manufacturers provide battery warranties of 8 years / 160,000 km with a 70% SOH threshold
As of September 2026, used electric vehicle prices are 20.3% below new ones
No SOH report, no purchase: a regular inspection report does not cover the battery

What is SOH, not to be confused with SOC

SOH summarizes the capacity a battery has lost over its lifetime in a single percentage. A new electric vehicle starts at 100% SOH; capacity loss through use and charging is a normal and irreversible process. This loss should not be seen as a defect - the point is to read whether the loss falls within a reasonable range for the age and mileage.

A common mistake is confusing SOH with SOC (State of Charge, i.e. charge level). SOC shows how full the battery is at that moment; it can be thought of as the electric vehicle's fuel gauge. The remaining range estimate on the screen also depends on SOC and current conditions: driving style, road surface and temperature change the result. Rather than relying on the range estimate as an exact measurement, you should look directly at the SOH data.

How to request an SOH report?

There are three basic ways to learn the battery health: an authorized service report, diagnostic apps via an OBD interface, and the information on the vehicle's screen. The most reliable of these three is an up-to-date authorized service report. If the seller avoids providing a report, accept that this is a warning sign in itself. A regular inspection report does not cover the battery; SOH and cell data obtained with a device are essential.

You can also have a test done yourself: the diagnostic device is plugged into the OBD port and collects voltage, temperature, charging history and current usable capacity data from the BMS, i.e. the battery management system, via the vehicle. Many test providers ask for a full charge or a specific drive for a more accurate result; the result can be sent by e-mail as a certificate. In Türkiye, there are also services that perform cell-based independent measurements - AVILOO certified measurement offers cell-level analysis and a fault report, while EVpertise provides independent cell-based measurement and a health certificate.

Which values should you look at in the report?

The SOH percentage is the single most important number, but reading the entire report increases your bargaining power:

Remaining usable capacity (kWh): The most direct measure of what you are buying.
Full charge range estimate: More practical for daily use planning than the SOH percentage.
Charge cycle count: Seeing a very high cycle count together with high SOH is unusual and should be noted.
Cell balance data: Serious imbalance can be an early sign of developing problems.
Maximum charging speed: May drop slightly with age; it affects your charging plan.

How should the SOH percentage be interpreted?

Evaluate the percentage not on its own, but together with the vehicle's age and mileage. A typical loss rate is about 2-3% per year; charging habits, climate and usage patterns change this rate. A practical framework looks like this:

SOH range	Interpretation
Above 90%	Perfect at any age; range is almost as good as a new car
Good;	Good; Typical for well-maintained vehicles aged 2-4 years
80-85%	Acceptable, but it should be reflected in the price; the loss is more noticeable in small-battery city cars
Below 80%	Should be considered carefully; may indicate above-average degradation or a history of heavy charging

Calculate your range expectation yourself: Multiply the official WLTP range by the SOH percentage, then apply an additional 10-15% discount for the difference between the official value and real-world conditions. As an example, a vehicle with a WLTP range of 400 km and an SOH of 87% can realistically be expected to deliver 300-312 km.

Does low SOH mean it's out of warranty coverage?

No. Most manufacturers provide battery warranty for 8 years / 160,000 km with a minimum SOH threshold of 70%. If the vehicle is still within the warranty period and the SOH has dropped below 75%, a battery replacement can be requested under warranty. In other words, a vehicle with a low SOH reading whose warranty is still valid is a vehicle for which this right should be checked before it is used as a bargaining chip.

Brands may report it differently: what should you pay attention to?

One of SOH's most sensitive points is the lack of standardization. Brands report SOH in different ways: Tesla and BYD derive SOH from the pack capacity, while others provide a normalized BMS health index. SOH values calculated with different methods and sources may not be comparable - so when verifying a seller's independent SOH claim, ask for the metric, the test method, the test date, the scope, the fault history, and the supporting report. The "not all SOH is equal" principle becomes especially critical when comparing two different vehicles.

Tesla: The data can be accessed from the vehicle's screen (Settings - Software); Third-party apps like Scan My Tesla provide cell-level data.
Kia / Hyundai: Authorized dealer diagnostic tools (GDS / GDS Mobile) produce a detailed SOH report, including cell balance.
Nissan Leaf: It can generate an authorized service report; the independent standard tool is the LEAF Spy with a compatible OBD adapter.
BMW / Mini: The ISTA diagnostic system in the dealership network provides comprehensive battery data.

In Türkiye, too, the process varies by brand; if possible, an authorized service report should be preferred, otherwise expert centers with equipment suitable for the model should be visited.

Traces of fast charging: why does the odometer lie?

Aynı 60.000 kilometre, iki çok farklı batarya demek olabilir; kilometreyi değil şarj alışkanlıklarını sorgulayın.

Mileage alone is a weak indicator of battery condition. Analysis of data from more than 22,700 vehicles shows high-power DC fast charging as the dominant stress factor leading to the highest annual degradation rate; in one study, drivers who used fast charging more than three times a month showed an additional 0.1% increase in degradation compared to those who never used it. Heat is one of the main contributors to degradation, and fast charging heats the battery.

The official figure should be read without exaggeration: occasional DC fast charging does not significantly damage the battery. The problem is frequent and exclusive use of fast charging. The practical conclusion is clear: a vehicle regularly used with DC fast charging to 100% is generally more degraded than a home slow-charged vehicle at the same mileage. The same 60,000 km can mean two very different batteries.

How do you recognize a repaired or reconditioned battery?

Cell balance data is the most advanced checkpoint at this point. Significant imbalance is an early warning sign of developing problems and must be reported to an expert. The second check is the consistency between SOH and the number of cycles: inconsistencies such as low SOH with a low cycle count or high SOH with a very high cycle count should be questioned. For example, a vehicle at 40,000 km with an SOH of 78% either carries a history of heavy fast charging or the report is unreliable - in both cases you should ask the seller for an explanation.

Also look at the date of the report: a document taken six months ago does not cover the usage from that day to today. A report with a current date, a clearly stated measurement method and cell data tells far more than the SOH percentage alone.

SOH in negotiation: how does price get affected in the Turkish market?

According to September 2026 data, used electric vehicle prices are running 20.3% below new ones, and buyers are advised to look at battery health, warranty and charging speed. In this picture, SOH is the most numerical tool of negotiation. If SOH is high, the seller may ask for a higher price, and that is deserved; if SOH is low and the vehicle is out of warranty, the low SOH must definitely be reflected in the price. Putting the interpretation framework above and the range calculation on the table for a vehicle in the 80-85% range carries the abstract negotiation onto measurable ground.

The overall health of the market is not worrying either: a large-scale assessment shows that electric vehicle batteries retain more than 93% of their capacity even after 70,000 km. So a low SOH is not automatically a problem; the problem is an unverified SOH. An SOH certificate is not mandatory for purchase and sale, but it builds trust - both seller and buyer benefit from it.

In short: checklist

Request an up-to-date SOH report with a known method and cell data; do not pay a seller who refuses to provide one.
Alongside the SOH percentage, read the kWh capacity, range estimate, cycle count, and cell balance.
Compare the vehicle's age against the typical 2-3% annual loss; below 80% is a serious reason to negotiate or walk away.
Check the warranty terms: the 8-year / 160,000 km and 70% SOH threshold may entitle a low-SOH vehicle to warranty coverage.
Ask about traces of fast-charging habits; base your judgment on the charging history, not the mileage.

The battery is the single most expensive component of a used electric vehicle. Buying it not on impulse but with a measured report is the simplest and most rewarding application of engineering logic.