Photo Credit: iStockSpec-sheet charging times grab attention, but the tougher question is what repeated ultra-fast charging does to a battery over time.Results from a punishing BYD trial point to a less alarming outcome than some EV owners might expect. As InsideEVs reported, Yangwang used a showroom U7 sedan for a nine-day test that included 350 fast-charging stops before checking the pack for degradation.Here's what to knowFor the experiment, BYD says it pulled a regular U7 from a showroom and pushed it to roughly 149 mph (240 kilometers per hour) at Nanning's test track, as Car News China first reported.AdvertisementAdvertisementBy the end of the nine-day run, the car had covered about 18,600 miles (30,000 kilometers), with BYD's Flash charging system used repeatedly along the way, per the outlet.Those repeated top-ups totaled 350 sessions, and the sedan reportedly accepted up to 640 kilowatts during charging. BYD said that once the test was over, the battery still had 98.7% of its original capacity, Car News China said.In 2025, BYD became a major force in the push for ever-higher charging speeds with its megawatt charging technology. InsideEVs reported that the newer setup can take vehicles from BYD, Denza, Yangwang, and Fangchengbao from 10% to 97% in as little as nine minutes.More backgroundFast charging has long raised durability questions. Battery packs can be strained by heat, frequent high-speed charging, and large bursts of power, fueling concern that added convenience might also mean more long-term wear.AdvertisementAdvertisementThe U7 was driven aggressively, charged heavily, and operated in average temperatures of about 97 degrees Fahrenheit (36 degrees Celsius), according to Car News China. That's the kind of hot-weather scenario that can put an EV's thermal management system under real pressure.Time itself also wears down batteries, InsideEVs caveated. A nine-day torture test can reveal a great deal about heat management and charging durability, but it cannot fully show how a battery pack will perform after years of ownership.What's being done?Automakers are trying to improve charging speed and battery durability simultaneously, and BYD's latest test suggests that thermal management is becoming just as important as headline-grabbing charging power.Faster, healthier charging can help reduce range anxiety, make apartment and public charging less frustrating, and keep commercial vehicles on the road instead of waiting in line at chargers.AdvertisementAdvertisementThere may also be broader benefits for cities and companies expanding charging networks. If vehicles can charge quickly without causing significant battery damage, each charger could serve more cars per day, improving convenience and potentially easing infrastructure bottlenecks.Based on tests like this one, extreme-speed charging may not necessarily come at the expense of battery health.Get TCD's free newsletters for easy tips, smart advice, and a chance to earn $5,000 toward home upgrades. To see more stories like this one, change your Google preferences here.
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