A Tesla Model Y recorded 99 percent battery retention after driving 16,000 miles, about 26,000 km, over six months even in a usage environment with a high share of fast charging.

InsideEVs reported on June 7 that a Canadian Model Y owner disclosed battery test results showing the vehicle retained 99 percent of its capacity compared with when it was new.

The case is drawing attention amid debate over electric-vehicle battery degradation. Frequent fast charging has generally been cited as a factor that can accelerate performance deterioration. The case shows battery condition may vary depending on charging method and management habits rather than fast charging itself.

The owner charged 2,588 kilowatt-hours using home slow charging and 2,888 kWh using DC fast charging over six months. By charged energy, fast charging exceeded slow charging. The owner carried out a separate battery test to confirm the result after an app tracking the vehicle's condition indicated there was no battery degradation.

The test began with the battery at 20 percent. The car was connected to an AC power source capable of supplying at least 5 kilowatts, and the system lowered the battery to near 0 percent before charging it back to 100 percent. A full charge took about 20 hours.

The test showed battery retention of 99 percent. That was higher than the 96 to 97 percent the owner expected. The displayed driving range on a full charge was 326 miles, about 525 km, the same as when the car was new.

The owner cited two charging habits behind the high retention rate. The battery was always preheated before fast charging, and the usual charging limit was set at 75 percent. The owner also said the battery was managed so it did not fall below 35 percent. The owner plans to continue combining home and public charging in the same way and to run the same test again in six months.

The case runs counter to claims that fast charging should be avoided unconditionally. It highlighted that even vehicles equipped with nickel-manganese-cobalt batteries can reduce degradation effects if the charging limit is kept below 80 percent and overly low state-of-charge ranges are avoided.

Even so, it is difficult to say the results alone settle the fast-charging debate because the case is based on six months of driving data from a single vehicle. Still, in line with existing observations that initial degradation tends to be relatively large in new batteries before gradually easing, it suggests that in real-world use, management habits such as preheating before charging, setting a charging limit and avoiding low charge can be important variables in battery condition, not only the frequency of fast charging.