D Grade
January 19, 2026
Alex KiersteinEV batteries degrade. How much, and why, are a matter of debate among EV advocates and reflexive haters. A new study adds a dash of objectivity.
The conventional wisdom, such as it is, about electric vehicles has evolved a bit since first-generation Nissan Leafs were chewing up batteries. We know that charging them to full, or letting them run fully empty, can hurt the battery. Hot weather and DC fast charging can also cause degradation. But how much is important, and that has not seeped into the broader public consciousness.
I follow EV news and have read lots of studies over the last few years showing that battery degradation isn’t an existential threat for most EVs in a typical vehicle service life. My neighbors, with strong opinions and less subject matter interest, have only retained the broadest strokes: EV and hybrid batteries can be frighteningly expensive to replace, and they can fail. It’s not clear to them how much fast-charging or state-of-charge hygiene affects the possibility of that outcome, in my experience.
That creates a huge information deficit my neighbors would have to overcome to take the leap. And a casual conversation with their car-guy neighbor isn’t usually enough. So until the sort of info that this study, by Geotab (a Canadian vehicle telematics and fleet management company), reveals becomes common knowledge, it never will be.
What I think is the most interesting aspect of the study is that it quantifies the difference between high-stress behaviors and normal behaviors. If you fast-charge a lot, exactly how much damage is that likely to do? Now I have a few data points to answer those questions.
First of all, a study is only as good as its dataset and methodology, and this appears to be a reasonable one. It’s not an owner-provided survey of a limited subset (owners who are willing to return surveys); Geotab looked at 22,700 EVs (with 21 different models, ranging from passenger cars to vans and trucks). It is almost certainly data gathered from fleet service, but there are many Chevy Bolts and Tesla Model 3s in fleets, so the data is also pertinent to private owners.
Geotab found a few broad trends worth highlighting.
The Impact of Fast-Charging
More fast-charging equals more degradation, and while it’s a significant difference, it is also not an existential threat to battery life. I will explain this in two ways using Geotab’s conclusions.
If you utilize fast chargers for less than 12% of your total charging sessions, Geotab found an annual degradation of 1.5%. More than that, and the average drops to 2.5%. The actual impact may be more or less, depending on the individual vehicle, because as Geotab points out, factors like the battery’s chemistry and how it is “tuned” for its application can also influence its life. (I.E., a battery optimized for power delivery in a heavy vehicle with large payload requirements may degrade faster anyways.)
But what does that mean in practical terms? Let’s pretend the average of the data is an individual vehicle. If you fast-charge it infrequently, your battery will degrade to roughly 95% capacity after 3.5 years. If you fast-charge it more than 12% of the time, it would degrade to … 91%.
The difference is statistically important but it also doesn’t affect the absolute functionality of the vehicle. I would argue that a 4% difference in capacity is going to be irrelevant to most consumers within that timeframe, except perhaps to slightly affect resale value in the wake of a battery health report. But quantifying the comparative impact also helps owners make conscientious charging decisions.
Charging Frequency
The raw frequency of DC fast charging has a small(er) impact. If you’re constantly topping up the battery, you’ll degrade slightly faster. And if you’re constantly refilling a significant amount of the battery’s capacity, that’s even worse. Those EVs that added a large amount of energy by fast charging frequently lost up to 3% capacity per year.
Very Full or Very Empty Batteries
Given the widely understood recommendation to keep batteries between 20 and 80%, it makes some sense that there will be a penalty for regularly putting an EV’s battery outside of those bounds. What Geotab found is that this factor has a lot of leeway thanks, it presumes, to automakers’ software controls that keep the batteries healthy. Only vehicles that spent 80% or more of their time (including driving, charging, and parked) at above 80% SOC or below 20% SOC saw a significant increase in degradation.
Geotab concludes that most drivers don’t need to worry about this as a factor. And considering that EV battery charging slows down significantly above 80% as cell balancing becomes a time-intensive process, few owners go to the trouble of waiting longer for a few extra miles anyway. If you’ve got a long trip planned, though, don’t stress about charging to 100%. Just don’t keep it there for a long time, or frequently.
Heavy Use vs. Light Use
Lastly, Geotab looked at throughput—basically, how hard the vehicle is used. How many charge and discharge cycles, the total quantity of electrons flowing into and out of the battery in the same period of time. As you might expect, heavy use equals heavier degradation. But here’s the thing: the difference between high-use and low-use is, again, small. A cycle is using and then refilling 100% of the battery’s usable capacity, not necessarily in a single session.
The study found that after 8 years of use, heavy-use EVs (cycles every 1 to 2 days) retained 81.6% capacity. Low-use retained 88%. That 7% is not irrelevant, but it’s also not disastrous.
The Bottom Line
Nothing in Geotab’s study appears to be concerning for everyday users of EVs for the sort of things that normal drivers do.
Now, if you’re a fleet manager looking at running a delivery service that would put extreme duty cycles on the vehicles, and that small amount of additional degradation makes things pencil out red, that’s one thing. But there are a lot of other things I would be concerned about when buying or recommending an EV, whether new or used, than degradation that will equate to less than 10% over the course of 8 years, which is roughly the normal ownership period.
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