Buying a used electric car: why mileage tells you almost nothing

When buying a petrol car, mileage is the main reference. On an electric car it says almost nothing: the motor barely wears, there is no gearbox in the usual sense, and brake pads last twice as long thanks to regeneration.

Everything hinges on one component — the traction battery. And it does not age from kilometres.

What battery condition depends on

Four factors, and mileage is not the first of them.

The number of full charge cycles. Not miles but cycles. A car charged daily from 20 to 80 % is less worn than one charged rarely but “from empty to full”.

The proportion of fast charging. Constant high-power charging heats the cells and accelerates degradation. A car that mostly used a home socket is in better shape than an identical one from a taxi fleet.

Temperature conditions. Heat does more damage than cold. A battery that stood in the sun for years without active cooling has lost more.

How it was stored. Long periods parked at full or near-zero charge age it faster than sitting at 50 %.

Hence the key conclusion: two electric cars with identical mileage can differ by 15–20 % in capacity, and nothing about that is visible from outside.

What battery health means

The parameter labelled state of health is the ratio of current capacity to the original. A new battery is 100 %; after a few years 90 %, 85 %, and onwards.

The practical meaning is simple: how much of the original range remains. 85 % on a car that did 250 miles when new means roughly 210 miles in ideal conditions, and noticeably less in winter.

The assessment logic is the same as on hybrids — covered in the hybrid battery health article.

What an ordinary adapter cannot show

Directness is required here. Traction battery condition is absent from the OBD-II standard.

The standard was built for emissions monitoring; on an electric car most of it loses purpose, and the battery was never part of it. The mechanics of that limit are in OBD on electric cars.

So assessing the battery requires one of two things:

1. Software that knows the specific make and model and can issue manufacturer requests.
2. An independent workshop check with the right equipment and procedure.

The cost of that check is the best investment you can make when buying an electric car. Without it the purchase is blind.

What an ordinary adapter does give

Not everything is pointless. Through the diagnostic port you can read:

12-volt system voltage. The most useful item available. A weak 12-volt battery is the most common real electric car failure, and it shows immediately at inspection. Covered in the EV 12-volt battery article.

Codes across every system, B, C and U series included. Network codes work exactly as on any car — see the U0100 guide.

The module roll call. Who answers and who does not. A missing module is a reason to establish why, just as on a conventional car.

Mode 09 — module VINs against the body VIN. A mismatch means the module came from another car; mechanics in its own article.

The inspection order

1. Arrange a battery check — first and foremost. Without it the rest is meaningless.
2. Ask about charging history: mostly a home socket or fast chargers. The difference in condition will be noticeable.
3. Look at the indicated range at full charge and compare with the factory figure.
4. Check 12-volt system voltage — 12.4–12.7 V overnight.
5. Read codes across every system.
6. Check the module roll call and their VINs.
7. Check paired accounts in the manufacturer’s app — the previous owner must be removed. Why that matters is in the cybersecurity article.
8. Inspect the charge port — contact condition, heat marks, mechanical damage.

Point 7 is the one most often forgotten, and it means a stranger retains the ability to unlock and locate the car.

What to watch on the test drive

• Regeneration behaviour — smoothness, whether it cuts out.
• How fast indicated range falls relative to distance covered.
• Climate system operation — on an electric car it is one of the largest consumers, and a fault hits range hard.
• Noises while driving — on an electric car you hear what an engine would mask: bearings, suspension, the reduction gear.

That last point is an advantage: diagnosis by ear works better here than on a conventional car.

In short

• Mileage is a secondary indicator on an EV; battery condition decides.
• Batteries age from cycles, fast charging, and heat — not from kilometres.
• Battery health is not in the OBD standard — you need brand software or a workshop.
• An ordinary adapter gives 12 V voltage, codes, the module roll call, and Mode 09.
• Confirming the previous owner is unlinked from the app is a mandatory separate step.

Download the app — voltage, codes across every system, the module roll call, and Mode 09 are read with an ELM327 adapter over Bluetooth SPP on Android.