Kia beats Tesla in battery capacity retention over time as used electric vehicles exhibit remarkable longevity

With used electric vehicle sales surging, a test of their battery capacity retention over time has returned some rather remarkable results when it comes to longevity.

Nearly 80% of the 723 electric cars and 643 plug-in hybrid vehicle tested managed to retain over 90% of their original battery's capacity after a few years when variables like charging level, atmospheric conditions, vehicle age, or mileage, have been averaged out.

Still, there are some EV brands that have tougher battery cells with advanced cooling and energy management technologies, which came out on top in the study that includes Swedish insurer KVD's three-star test system to determine their batteries' State of Health (SoH).

Kia makes the toughest, longest-lasting batteries with the highest capacity retention over time, both in their electric vehicles like the EV6, and in plug-in hybrids like the Sportage SUV. Another Kia vehicle took the second spot in the best battery capacity retention over time ranking, and was immediately followed by the Model Y, despite that Tesla cars come with much slower charging speeds compared to Kia or Hyundai.

Tesla's second place in the ranking of the best EV brands when it comes to battery health is important, since the Model Y sells in much higher quantities than other brand models in Europe where the battery longevity test was carried out. This is despite the significant drop in Tesla sales there this year due to Elon Musk's political activism and the influx of BYD and other Chinese brands there.

There are a few important pointers when it comes to realizing an EV battery longevity potential, according to KVD's Martin Reinholdsson:

• Don't charge your battery fully often: try to keep the battery's charge between 20 and 80 percent during everyday life, and save a 100 percent charge for just before longer trips.
• Avoid extreme heat and cold: protect your battery from extreme temperatures by parking it cool when it's hot, preheating the car when it's plugged in the cold and using any battery preconditioning.
• Fast charge rarely: use fast charging when needed, but not all the time; avoid fast charging an ice-cold battery and top up with the charger at home before leaving.
• Don't leave your car fully charged: don't leave your car parked for long near 0 or 100 percent, and if it's going to be parked for more than two weeks, leave it around 40–60 percent and turn off energy-intensive functions.
• Set a charge limit: take advantage of your car's software support by setting a charge limit (for example, 80 percent), scheduling charging so that it's ready close to departure and keep the software updated.

The used EV market has never been as dynamic and varied, with the second-hand vehicles' battery SoH emerging as a key purchase indicator. Kia gives a 7-year or 150,000 km "boot-to-bonnet" warranty in Europe, including the battery and drivetrain, while Tesla's basic vehicle warranty is four years and 80,000 km, with an 8-year warranty only going to the battery itself. In the US, however, Kia's battery warranty is the class-leading ten years.

Both automakers only guarantees that the battery will retain at least 70% of its original capacity during that time, while Chinese brands are now striving to standardize 15-year battery warranties at 85% capacity retention. The world's largest battery maker CATL is already giving 12-year battery warranty for NIO's swap stations, and 20-year for some LFP energy storage units, so the chemistry seems to be already there.

The biggest EV battery recycler in the US, Redwood Materials, has pegged current EV batteries as good for at least 15 years, so their longevity potential exhibited in the new study is not all that surprising. Still, official battery warranties need to be significantly lengthened if the used EV market is to become as dynamic as the ICE vehicle one.

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