A new study looked at 6,300 electric cars, and it was clear what led batteries to degrade quicker.
Like so many moving parts in an engine, batteries aren't designed to last forever. Thankfully, new research shows the typical electric car batteries degrade at such a slow rate that they'll outlive the usability of the car they're installed in.
A new study from fleet-management company Geotab looked at 6,300 electric vehicles to understand how quickly EV batteries degrade. On average, an EV saw its battery degrade 2.3% each year, which is so minor it doesn't reflect an outright reduction in usable range. Without going into the wild math and innards of a battery, if the average battery's energy storage declines by 2.3% every year, over five years that's only a loss of 15 miles of driving range in an EV with 150 miles of total range.
Overall, numerous things can affect a battery's state of health, ranging from usage to temperatures. While the study looks at many areas, in the 6,300 electric cars observed, there were two major factors that sped up battery degradation: DC fast charging and how an automaker engineered its cooling solution.
DC fast charging is the preferred way to juice an electric car up quickly. Otherwise, drivers are stuck with a 240-volt outlet (Level 2 charging) or a standard 120-volt outlet (Level 1 charging), which can take hours to charge. The study showed EVs that exclusively charged on L2 and L1 chargers saw very little degradation, while the more an EV was subjected to DC fast chargers, the more battery degradation occurred.
That can be explained by the presence of high electrical currents and high temperatures -- not the healthiest things for any battery. L2 charging remains the most efficient way to charge an EV, but DC fast charging is certainly the quickest way.
As for thermal management, there was a big difference between electric cars that used air to cool the battery compared to liquid cooling. Comparing a 2015 model year Nissan Leaf, which uses a passive air-cooling system, to a 2015 Tesla Model S, which uses liquid cooling, the Leaf saw 4.2% degradation in a year versus 2.3% for the Model S. Again, higher temperatures lead to more degradation.
You can head to the study here, and play with a wonderful tool that includes every electric car sold thus far, to see how its degradation stacks up against others and the average figure.