How to check a used EV’s battery before you buy: SoH, OBD apps, certificates and warranty
A practical guide for anyone buying a used EV in Romania: what SoH means, how to read battery health with an OBD adapter, which certificates to ask for, what the warranty covers, and what to check on the test drive and at a fast charger.
In an electric car, the battery is the most expensive part, so its condition matters more than almost anything else on a used car. And in Romania, many EVs arrive used: for Tesla alone, 987 of the 2,446 cars registered in the first half of 2026 were second-hand, according to DRPCIV data analyzed by Plus-Auto.ro.
What SoH means
SoH (State of Health) shows how much capacity the battery has left compared with when it was new. An SoH of 90% on a 60 kWh battery means it can still store about 54 kWh, so range drops roughly in proportion. Don't confuse SoH with the state of charge (SoC) shown on the dashboard.
1. Ask for a battery certificate
The easiest option is a report made by someone other than the seller:
- AVILOO runs independent tests. The quick FLASH test takes a few minutes through the OBD port and ends with a certificate sent by email. AVILOO calculates its own SoH rather than just copying the car's figure, and flags anomalies.
- Renault and Dacia offer a digital battery certificate for connected models through the My Renault app.
- For other brands, you can ask for a diagnostic report from an authorized service center before signing the contract.
A certificate shows the battery's condition on the day of the test; it doesn't predict how long it will last.
2. Read the battery yourself with an OBD adapter
You need a Bluetooth OBD2 adapter (from a few euros to several dozen) and an app that suits the brand:
- Car Scanner: works with many EVs, including Hyundai and Kia, and shows the SoH the car reports.
- LeafSpy: the standard for the Nissan Leaf. It shows SoH, the number of fast charges and each cell's voltage.
- Scan My Tesla: shows the battery's actual capacity ("nominal full pack," in kWh), which you compare with the value when new.
Some Teslas also have an official test under Controls > Service > Battery Health. But Tesla removed it from many cars in 2025, and the test takes up to 24 hours and requires charging to 100%, so you can rarely run it at the seller's.
3. Check the battery warranty
The battery warranty runs from first registration and passes to the new owner. At Tesla, for example, it's 8 years or 160,000 km on the Model 3 and Model Y Standard (192,000 km on Long Range and Performance), with at least 70% capacity. Most major brands also offer 8 years and 160,000 km, while Kia offers 7 years or 150,000 km. A car still under warranty is much safer: if the battery drops below the threshold, the manufacturer repairs or replaces it.
4. The test drive and a fast charge
- Start with the battery as full as possible and compare the displayed range with that of a similar car. For the gap between rated and real-world range, see our WLTP guide.
- Drive on a fast road too and watch how quickly the percentage drops.
- If you can, stop at a DC fast charger with the battery below 30%. Power well below normal for the model and temperature can point to a problem. What's normal is covered in our charging curve guide.
Red flags
- The seller won't let you plug in an OBD adapter or charge the car.
- Dashboard warnings about the battery, reduced power or the charging system.
- Large voltage differences between cells (in LeafSpy or Car Scanner).
- A "replaced" or "refurbished" battery with no invoices from a service center.
- On the Leaf, whose battery has no active cooling: lots of fast charging and a car imported from a hot country.
In short: ask for the certificate, read the SoH with an app, check the warranty and do at least one fast charge before you hand over the money.
