Driving Your EV Like A Lunatic Might Help Its Batteries Last Longer: Stanford Study

One of the big fears of buying an electric car to keep for the long-haul is battery degradation. After a slight initial drop in performance, battery condition should level off for years, but when will performance decline again? As it turns out, it might take longer than previously thought. Researchers at the SLAC-Stanford Battery Center have spent two years trying different charging and discharging profiles on lithium-ion battery packs and have found that realistic charging/discharging cycles — including quick bursts of acceleration — may result in way slower battery degradation than expected.

As Automotive News reports:

The researchers found, according to their paper published Dec. 9 in the Nature Energy scientific journal, that the batteries subjected to more dynamic charging and discharging cycles scored better on battery health metrics such as the amount of lithium or the degradation of electrodes.

From the Stanford Report:

Simona Onori, senior author and an associate professor of energy science and engineering in the Stanford Doerr School of Sustainability […said:]“To our surprise, real driving with frequent acceleration, braking that charges the batteries a bit, stopping to pop into a store, and letting the batteries rest for hours at a time, helps batteries last longer than we had thought based on industry standard lab tests.”

Alright, so what does this mean? Well, most batteries are lab-tested for degradation by constantly pumping energy in and out of them. It’s a way to accelerate testing so that thousands of charging cycles don’t take years to happen, but it’s not how privately owned electric cars are used. Instead, actual electric cars see dynamic charging/discharging, periods of rest between drives, and those charged at home often also see periods of rest between reaching a full charge overnight and setting off in the morning.

The scientists at SLAC-Stanford Battery Center call this dynamic cycling, and it turns out that real-world usage may result in much longer battery lifespans than people previously thought. As the study reports, it can result in as much as a 38 percent longer battery lifespan than seen under constant current testing. This is particularly interesting because all this real-world cycling was previously thought to be more harmful to batteries than constant current lab testing. As per Stanford:

The research team tested 92 commercial lithium-ion batteries for more than two years across the discharge profiles. In the end, the more realistically the profiles reflected actual driving behavior, the higher EV life expectancy climbed.

In fact, that’s where the findings only start to get interesting. Are you addicted to the thrill of jackrabbit EV acceleration? Believe it or not, those rapid discharge events might actually be good for your battery. As Stanford reports:

For example, the study showed a correlation between sharp, short EV accelerations and slower degradation. This was contrary to long-held assumptions of battery researchers, including this study’s team, that acceleration peaks are bad for EV batteries. Pressing the pedal with your foot hard does not speed up aging. If anything, it slows it down, explained Alexis Geslin, one of three lead authors of the study and a PhD student in materials science and engineering and in computer science in Stanford’s School of Engineering.

As you can imagine, this revelation — which, it’s worth noting, comes from just this one Stanford study — has caused an exciting stir on some EV forums.

It’s worth noting that there may be limits to this. Batteries generally don’t like heat, and repeated hard acceleration can put serious thermal stress on an EV’s battery pack. Quick bursts of acceleration in between sustained cruising might be helpful, but repeated quarter-mile drag strip runs might not carry the same supposedly helpful properties.

If you’re wondering exactly how much longer battery packs last in the real world than we expected in testing, the truth is that we don’t actually know with precision. On the one hand, some actively-cooled battery packs in early modern EVs have fallen below a degradation threshold that necessitates replacement. Our own David Tracy experienced this with his first i3. On the other hand, there are still a bunch of early Tesla Model S sedans roving around on their original battery packs, and those are knocking on the door of 13 years old. Battery chemistry, management, and thermal conditioning has only improved since then, so it’s looking more plausible than not that today’s crop of EVs will make fine beaters in 20 years.

[Ed Note: While my first model-year i3 (60Ah model) did suffer from battery degradation over 135,000 miles, it has a small battery hooked to a range extender, so it saw lots of charge/discharge cycles (in a hot climate, too) and the battery was often at low states-of-charge as the range extender often struggled to keep it from dipping below 6.5 percent. My newer BMW i3, the 120 Ah model, should last much longer, as some testing by others has shown negligible degradation after five years and almost 100,000 miles. That’s impressive! -DT].

So does this mean that you should be able to buy an EV and keep it basically forever with maybe one battery pack replacement once it hits 30? Well, not quite.

Although the battery packs may see less degradation than expected, a bad battery pack isn’t the only thing that can send a car to the scrapheap. Twenty years down the line, it’s possible that replacing something expensive like a panoramic sunroof or expensive air suspension components could render an electric vehicle mechanically totalled, just like it might a combustion-powered car. In addition, parts support tends to dwindle as cars age, so it’s possible that the critical part you need in 20 years, like an encrypted module programmed by the manufacturer, might simply no longer be available. Lastly, in the rust belt, rust will still be a factor for how long a vehicle’s kept on the road. If your electric vehicle’s made out of steel and you drive on salt-brined roads, it might rot out before anything propulsion-related goes really wrong. You know, like a late-’90s Honda.

Anyway, it’s kind of neat to know that — in the real world, and with quick accelerations/battery discharges every now and again — EVs might last longer than previously expected based on testing. Will old ones be janky in the future? Sure, but the majority of them probably won’t be paperweights like David’s old Nissan Leaf with its highly questionable air-cooled battery pack.

(Photo credits: Hyundai, Honda, Tesla, Kia)

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