Mileage has always been one of the first numbers used to judge a used car. With an electric vehicle, however, that familiar number may tell you surprisingly little about the condition of its most expensive component.
Two identical used EVs can arrive at the same dealership showing exactly the same distance on their odometers while hiding substantially different battery health. From the outside, there may be no obvious clue which one has aged better.
That’s important to know, because battery condition directly affects usable range, long-term ownership costs, and, ultimately, what a used EV should be worth. Judging one purely by mileage risks overlooking a major part of the picture.
A new analysis from battery diagnostics company AVILOO illustrates just how wide those differences can become. After examining more than 500,000 independent battery tests, the company says individual examples of the same model can vary dramatically even at identical mileage.
Same Mileage, Very Different Batteries
AVILOO analyzed results from its FLASH Test database covering 20 popular EV models tested between 2022 and 2026. The data spans North and South America, Europe, Asia, and Australia, with battery State of Health, or SoH, compared at 50,000, 100,000, and 150,000 kilometers.
At 50,000 km, roughly 31,000 miles, median battery health ranged from 91.2 percent for the Nissan Leaf ZE1 to 97.1 percent for the Hyundai Ioniq 5. More importantly, AVILOO found that individual examples of the same model could already be separated by as much as 10 percentage points.
The gap becomes even larger with mileage. AVILOO says the spread within individual models can reach 13.3 percentage points at 100,000 km (62,000 miles) and as much as 16.4 points by 150,000 km (roughly 93,000 miles).
The Ioniq 5 And Leaf Tell Different Stories
Among the four vehicles AVILOO examined in greater detail, the Hyundai Ioniq 5 consistently recorded the strongest median battery health. It retained 97.3 percent at 50,000 km, 95.1 percent at 100,000 km and 93.4 percent at 150,000 km.
The Nissan Leaf ZE1 sat at the opposite end, dropping from a median 90.8 percent at 50,000 km to 85.9 percent at 150,000 km. AVILOO notes that its relatively small 40-kWh battery also tends to experience more charging cycles, which can contribute to faster degradation.
The Tesla Model Y landed between those extremes, with median SoH falling from 94.5 percent to 90.1 percent across the same mileage range. At 150,000 km, AVILOO found a 46-km difference (28.6 miles) in real-world range between the strongest and weakest Model Y examples.
Mileage Isn’t The Whole Story
Battery aging depends on considerably more than distance traveled. Climate, charging behavior, battery size, cell condition, and the number of charging cycles can all influence how much capacity remains.
AVILOO’s three-minute FLASH Test connects through a vehicle’s OBD port and uses diagnostic data, including mileage, age, cycle count, cell-voltage spread, and energy counters. The company says it calculates battery health independently rather than simply repeating the figure reported by the vehicle’s own battery-management system.
That distinction is important for used-EV shoppers, as a low-mileage car may have a weaker battery than a higher-mileage example that has been treated more gently.
Used EV Buyers Need Another Number
AVILOO CEO Dr. Marcus Berger says the key lesson is that averages can conceal substantial differences between individual cars. Even if a particular model generally performs well, there is no guarantee a specific vehicle sits near that average.
For buyers, dealers, and lenders, that makes battery health increasingly important when valuing used EVs. Mileage and service history are still relevant, but neither can reveal exactly how much usable battery capacity remains.
The odometer, therefore, isn’t becoming irrelevant, but it simply isn’t enough on its own. When shopping for a used EV, an independent battery-health result may tell you far more about the car you’re actually buying than the mileage displayed behind the steering wheel.