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For many years now, it has been advised to not fast charge electric vehicles too much, that doing so could lead to rapid degradation of your EV’s battery. It’s always been unclear how much this matters, though, and especially across different vehicles with different battery management systems. At times, Tesla CEO Elon Musk and former CTO JB Straubel have said not to worry about it, and to Supercharge as much as you need. At other times, it’s been recommended that you only do it on road trips and that you not rely on it for all your charging. As someone who has done 85% of my charging at Superchargers in the past year (and 90% in the past month), I have of course hoped that “it’s not such a big deal” is the correct answer. According to recent research, that is indeed the case!

One key point is something I learned from Mark Z. Jacobson years ago during dinner is that batteries degrade quite a bit early on, when they are new, and then degradation is often minimal for years (or even well beyond a decade), and then there’s another significant drop much later on. JB Straubel estimated several years ago that Tesla EV batteries would probably retain good capacity (not see more than 30% capacity degradation) for 15+ years. Recurrent Auto’s Liz Najman summarizes it like this: “Degradation is not linear. We’re including battery degradation curves that illustrate how well these batteries hold up over time. There’s some drop in the beginning then it levels out for a long period.”

Najman is also honest about the fact that we still don’t know a lot. “How long is that EV battery going to last? The one simple answer is that we don’t know for sure because electric cars have not been around long enough for us to tell. The best we can do is observe the apparent degradation in those cars on the road.” That’s what I often say when people ask (or simply comment) about EV battery lifespan. She adds:

“Coming up with an exact answer to what a battery lifetime is complicated because:

1. Batteries are complicated systems. We can’t observe them directly, and have to rely on a computer interface to give us information about their state of health, state of charge, and more.
2. We know more about battery cells than battery packs. Most of the rigorous scientific tests on lithium ion batteries are done on individual battery cells, not the high-tech systems used in EVs.”

Indeed.

The useful thing with Recurrent Auto is that it’s got a community of 15,000 electric cars. In that article, you can dig in much more to how batteries have degraded in different EV models.

More recently, though, Recurrent Auto published another article just on the impact of EV fast charging. Blake Hough starts the article like this: “One of the biggest concerns with fast charging is that it can, theoretically, damage the battery by pushing too much energy into your car too quickly. This would lead to irreparable, long-term range loss.” However, to test this out, researchers dug into the effect of fast charging on 12,500 Tesla vehicles. While the company still recommends that occasional fast charging is fine but not necessarily frequent fast charging, the results showed no statistically significant difference in battery degradation between Tesla Model 3 vehicles that charged at least 90% of the time using Superchargers and Model 3 vehicles that charged no more than 10% of the time using Superchargers. Yay for me! The same was the case for Model Y vehicles.

Interestingly, looking at the graphs (Model 3 here and Model Y here), Model 3 vehicles and especially Model Y vehicles that rarely Supercharged had lost more battery capacity, or range, over the same period of time as Model 3 vehicles and Model Y vehicles that frequently Supercharged. However, remember that the difference isn’t statistically significant, so don’t read into that. I’m just highlighting this surprising result to emphasize that the opposite should not be a concern.

The issue is that much research on battery degradation has been done on battery cells, inherently ignoring the work battery pack producers and automakers have done to limit any effect of heat and fast charging on cells. It turns out, those efforts have actually paid off. Cells are protected, and fast charging doesn’t seem to have any effect on the long-term health of batteries. “In short, the robust thermal, voltage, and battery management systems that EV makers have invested in do protect their batteries from damage with routine fast charger use,” Hough writes.

Again, this is a relief for those of us who have relied on a lot of Tesla Supercharging, but I’m still not encouraging people to go fast charge more — if you don’t have a good reason for it. We had no home charging options with my 2019 Tesla Model 3 for a couple of years. In the past couple of years, meanwhile, I’ve just not been eager to charge at home instead of using free Supercharging — even though that would be more convenient. At long last, though, after 4+ years of this, I can finally be completely guilt free when using the Superchargers! I also find comfort in the fact that these are still 150 kW Superchargers, which are not as fast as newer ones (but still a bit faster than I’d generally prefer).

What do you think about this research and the general theory and discussion of the topic? Do you see the findings as convincing enough — for now, at least? Or do you see some flaws in the research and findings? I’m happy to hear all opinions, as long as you don’t ruin my newly elated view of Supercharging!