STOCKHOLM—A comprehensive study of electric vehicle (EV) battery health in Sweden has found that the Kia e-Niro and Hyundai Kona Electric retain more than 97% of their original battery capacity after 100,000 kilometers (approximately 62,000 miles). The findings, based on 9,954 real-world battery tests conducted by Swedish used-car marketplace Carla between 2022 and 2026, provide one of the largest datasets to date on long-term EV battery performance.
Leading Models and Industry Benchmarks
The Kia e-Niro, marketed as the Niro Electric in the U.S., topped the rankings with an average battery retention rate of 97.25% for its 64-kWh pack. The Hyundai Kona Electric followed closely at 97.18%, outperforming newer and higher-performance models in the study. Both vehicles utilize liquid-cooled battery systems with charging rates limited to below 80 kilowatts (kW), a design choice that Carla’s analysis suggests may contribute to reduced heat stress and slower cell degradation.
Other models in the top 20 demonstrated similarly strong performance, with degradation rates consistently below 10%. The Kia EV6, despite its 800-volt architecture and faster charging capabilities, retained 95.95% of its 77.4-kWh battery capacity. The BMW i3 (42.2 kWh) and Tesla Model 3 also performed well, with retention rates of 93.77% and 94.35%, respectively. Even the lowest-ranked vehicle in the top 20, the Volkswagen ID.3, maintained 91.79% of its original capacity after the same mileage.
Factors Influencing Battery Longevity
Carla’s analysis highlights several technical and environmental factors that may explain the strong performance of the tested EVs. Sweden’s cooler climate is likely to have played a role, as lower ambient temperatures reduce thermal stress on battery cells. However, the study also notes that advanced battery management systems and thermal regulation—such as those in the Kia EV6—can mitigate the effects of faster charging, which typically generates more heat.