The Battery Health Document That Protects Your Purchase

Buying any used car carries risk, but when it’s electric the single most expensive component – the drive battery – is also the hardest to assess from the outside. That’s why the German initiative “Safe Car Purchase Online” (ISAK), backed by the ADAC, AutoScout24, Kleinanzeigen and mobile.de, insists that every used‑EV buyer ask for a battery health certificate. The document reports the battery’s State of Health (SoH), expressed as a percentage of its original capacity.

As a rough guide, the ADAC’s collected data suggest that a well‑treated battery should still deliver at least 92 % of its original capacity at 50,000 km, 88 % at 100,000 km, 84 % at 150,000 km and 80 % at 200,000 km. A car that falls noticeably below these benchmarks may have been subjected to particularly heavy use or charging abuse – a warning sign that the second‑hand price should reflect.

Even a strong SoH figure, however, doesn’t tell the whole story. The official WLTP range is a laboratory number; real‑world consumption depends on driving style, outside temperature, and use of heating or air conditioning. The previous owner’s daily experience therefore matters at least as much as the certificate. How far did the car actually go on a full charge? How was it usually charged – mostly at a wallbox between 20 % and 80 %, or frequently at ultra‑fast DC stations? Answers to these questions help you gauge whether the battery has been pampered or punished.

What the SoH Numbers Really Tell You About Range and Long‑Term Costs

Understanding the ADAC Mileage Benchmarks

The State of Health percentages supplied by the ADAC are not a guarantee but a statistical yardstick. They reflect what the club’s engineers typically measure in vehicles that have been driven normally and charged sensibly. If a used EV you’re inspecting shows a notably lower SoH for its mileage, it doesn’t automatically mean the battery is about to fail – but it does mean you have negotiating power, because a battery with, say, only 78 % health at 100,000 km will offer less usable range every day and will reach the 70 % threshold – where many manufacturer warranties kick in – sooner than an average car. Critically, the certificate itself matters: a test report from the ADAC, TÜV or Dekra carries far more weight than a verbal assurance from the seller.

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Why Real‑World Range Differs from the Certificate

A SoH reading of 90 % may suggest the car can still deliver about nine‑tenths of its original range, but the actual miles you’ll get are always lower because battery capacity is only one factor. Cold weather, motorway speeds, and cabin climate control can each cut range by 20–30 %. That’s why prospective buyers should ask explicitly what distance the previous owner typically covered in winter and summer, not just rely on the SoH. Also, charging habits leave a lasting mark: regular fast‑charging with direct current (DC) speeds up chemical ageing, while keeping the battery routinely between 20 % and 80 % is gentler. A seller who can’t or won’t discuss charging patterns may be hiding knowledge of accelerated wear.

Your Step‑by‑Step Checklist for a Used EV Inspection

Before you sign, go through these checks – all backed by the specific points raised by ISAK and the ADAC:

  • Ask for a battery health certificate from an independent testing organization (e.g., ADAC, TÜV or Dekra). The document must show the SoH as a percentage of original capacity.
  • Compare the SoH against the ADAC’s field‑experience benchmarks: at least 92 % at 50,000 km, 88 % at 100,000 km, 84 % at 150,000 km and 80 % at 200,000 km. A lower figure should be reflected in the purchase price.
  • Check whether the manufacturer’s battery warranty – often eight years or 160,000 km – is still valid and transfers to a second owner. Confirm the exact capacity threshold (commonly 70 %) that triggers a free repair or replacement.
  • Ask the seller: “What real‑world range did you get in everyday use, in summer and in winter?” and “How was the car charged most of the time – overnight wallbox, public AC, or frequent DC fast‑charging?”
  • Make sure all original charging cables, the service booklet and any recall documentation are present. Missing equipment can cost several hundred euros to replace.
  • Use a written purchase contract that explicitly records the battery’s condition. The ADAC provides a free template designed for used electric vehicles.