Frequent EV fast charging should cause a battery to degrade. Based on laboratory experiments and a solid understanding of how lithium ion batteries age, scientists have long known that frequent high voltage charging can speed up battery degradation and range loss. But how does that laboratory science translate to lithium ion battery packs in EVs?

Recurrent looked at fast charging in 13,000 Teslas on the road in the US, expecting to see that vehicles that mostly fast charge have statistically lower range and more degradation than vehicles that fast charge infrequently. 

We thought we’d see something like this:

This is what scientists expected to see

Instead, to our surprise, our analysis of more than 160,000 data points found that there was no statistically significant difference in range degradation between fast charging more than 70% of the time and fast charging less than 30% of the time. At least not yet.

In the chart below, the blue curve shows the observed range one standard deviation above and one standard deviation below the mean for cars that fast charge less than 30% of the time. The orange curve shows the same but for cars that fast charge at least 70% of the time. The fast charging is not having the negative effect we expected.

Note: since there are so many fewer cars that fast charge often, the orange curve is noisier and has more irregularities. 

Is EV battery age a factor here?

‍Our data looks at 2012 - 2023 model years, but 90% of the vehicles are from 2018 or later and 57% are from 2021 or later. The data skews heavily towards newer cars. In effect, we are looking at what fast charging does over 5-6 years. We do not know if there is a cumulative effect that will be seen in these batteries’ futures.

Moreover, we do not have historical charge data on older cars to know if their range has already been impacted.   

One thing we did see was that all Tesla batteries - fast charged and not - do show range degradation over time. And that’s OK! Lithium ion batteries do degrade with age and use. In the plots below, you can see similar levels of range loss in two different values: 

  1. the dashboard range, or what the driver sees in their car, and 
  2. the Real Range, a Recurrent value based on observations that takes factors like terrain and weather into account. 

Like in the plots above, the larger, standard deviation band for the Real Range shows that there is more variability in that number. We’d expect this since Tesla generally keeps the dashboard range pretty tightly controlled to provide a consistent experience for the driver. 

So, should you fast charge without concern?‍

Keep in mind that the vehicles we observed are relatively young and we do not know how these fast charged batteries will continue to age. If you plan to hold on to your EV for the long haul, you may still want to save high voltage charging for road trips.Other good ideas? Try to avoid fast charging when your car battery is very hot, very cold, or at an extreme state of charge - such as 5% or 90%. All of these situations can put extra stress on the battery and the BMS.

DC fast charging: fact or fiction?

Fiction
  • Routinely fast charging your car from 0-100% is fine.
  • The kilowatt (kW) rating of a fast charger controls how fast an EV can charge at it.
  • Any amount of fast charging will cause permanent damage to your battery.
  • Fast charging in the cold will cause lithium plating.
Fact
  • Almost all electric vehicles have software that will curtail fast charge speeds above 80% state of charge. In fact, it’s usually recommended to switch to a level 2 charger for the last 20%, as it may be as quick - or quicker.

    A level 2 charger, even a public one, is often cheaper, too.
  • In each different EV model, software and battery limitations control how fast the car can charge. Charge speed is also dependent on temperature, state of charge, and even battery age.
  • It’s still difficult to quantify precisely how much routine fast charging affects battery health long term – 5, 10, 20 years – but it’s fine in small doses.
  • EV batteries have a lot of software and hardware to protect them and ensure they are the right temperature before accepting high voltage to avoid lithium plating.

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