Worried about a used EV’s battery? Here’s how to check it before you pay

The battery is the reason most people hesitate over a used EV, and it’s the one part of the car you can’t inspect by looking at it. The good news is that a reading exists, it takes about five minutes to get, and it costs less than a set of tyres. The harder part is knowing what the number means once you have it.

What is state of health, and why does it matter?

State of health is the percentage of its original capacity a battery still holds, so a pack reading 88 per cent stores 88 per cent of the energy it did when new. It matters because it translates straight into range and into what the car is worth, and because the Electric Vehicle Council says every battery loses some capacity over its life.

Degradation is normal and it’s gradual. The Electric Vehicle Council, the national body for the EV industry in Australia, sets the rate by four things: the battery’s chemistry, the temperatures it lives in, how the car is driven and how it’s charged. Batteries don’t usually fail. They fade.

How far they fade before the car is finished with them is the part buyers get wrong. The Electric Vehicle Council expects EVs sold today to last around 15 years in the car, with a working battery life equivalent to roughly 200,000 kilometres of driving, and it says a pack pulled from a car can then serve another 10 or more years as stationary storage for a home or the grid before it’s recycled. A three to six year old EV is nowhere near the end of that curve.

The scale of the evidence helps here. Geotab, a fleet telematics company, analysed real-world data from more than 22,700 electric vehicles across 21 models and found an average loss of 2.3 per cent of capacity a year, as set out in its EV battery degradation study. At that rate a battery still holds about 81.6 per cent of its original capacity after eight years. Geotab’s conclusion is that modern EV batteries typically outlast the vehicles they’re fitted to.

What makes one battery degrade faster than another?

Charging behaviour is the biggest thing the previous owner controlled, and the gap it creates is large. Geotab found vehicles that regularly used DC fast charging above 100kW lost 3.0 per cent of capacity a year, against about 1.5 per cent a year for vehicles that mostly charged at lower power. That’s roughly double, from the same cars doing the same job.

So ask the question directly. An EV that lived in a garage on a home charger overnight has had an easier life than one that belonged to a rideshare driver topping up at public fast chargers between fares. Neither is disqualifying, but the second one should read lower for its age, and if it doesn’t, be curious about why.

The Electric Vehicle Council puts the same idea more plainly: the harder a battery works, the quicker it degrades. Heat, heavy loads, towing, sustained high-speed running and repeated fast charging all count as working hard. A commuter car that did 60km a day on a suburban round trip has not worked hard, whatever the odometer says.

How do you get a battery health reading?

You get a real reading by having a diagnostic tool plugged into the car, because the pack’s own cell data is the only honest source. Everything short of that is an estimate.

The most accessible option in Australia is the NRMA’s EV battery health check, which costs $250 for My NRMA Rewards members and $300 for everyone else. A patrol officer comes to wherever the car is, plugs in a small diagnostic tool, and the test itself takes about five minutes, with the results emailed almost immediately, according to the NRMA’s guide to checking EV battery health. You get a score out of 100, the battery’s current capacity, and a note of anything that might affect performance or lifespan.

Three limits are worth knowing before you book, all of them stated by the NRMA. The tool works with over 90 per cent of electric and plug-in hybrid vehicles sold here, but not with conventional hybrids. The service currently runs only in Sydney metropolitan areas and Canberra, weekdays from 8am to 4pm, and needs to be booked online with 48 hours’ notice. And the check doesn’t replace full manufacturer diagnostics or guarantee how the battery will perform in future.

If the car is outside that service area, ask the selling dealer or a marque specialist to pull a state-of-health reading from the car’s own systems. In the meantime, two rough checks cost nothing: note the range the car predicts on a full charge against its original rated range, and look through the infotainment service menus, since several brands display a battery health figure there.

What number should make you walk away?

There isn’t an official one, so judge the reading against the car’s age rather than a fixed threshold. The NRMA reports remaining capacity and a score out of 100 but doesn’t publish a walk-away figure, and no other Australian body does either.

Use the industry average as your yardstick. On Geotab’s 2.3 per cent a year, a three-year-old EV should be somewhere near 93 per cent and a six-year-old one near 87 per cent. A car sitting a couple of points either side of that is behaving normally. A four-year-old car reading in the low 80s has either been fast-charged hard or has a problem, and the seller should be able to tell you which.

Then work out what the shortfall costs you. On a car with 400km of original range, a reading of 85 per cent means about 340km today, easing further at the 2.3 per cent a year Geotab measured. If that still covers your longest regular trip with room spare, the reading is a negotiating point rather than a reason to walk. If it doesn’t, no discount fixes it, because you’d be buying a car that can’t do the job.

Best for buyers who can get the car tested before handing over money and who have a home charger for overnight top-ups. Not for anyone buying sight-unseen at auction, where you get no reading and no recourse. The NRMA’s $250 member price is the cheapest part of a used EV purchase, and the part that turns the battery from a worry into a number you can argue about.