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New Data Shows Heat & Fast-Charging Responsible For More Battery Degradation Than Age Or Mileage

Lots of people are concerned about how quickly the battery in an electric car degrades. Data collected by GeoTab suggests there is little to worry about, but fast charging may be an issue.

We recently got an email at CleanTechnica world headquarters from a reader who wondered what we knew about battery degradation. The answer was, not much. Several of the ace reporters who labor here everyday own electric cars, most of them Teslas, but the truth is none of us has ever had a battery related issue with our cars. We just drive them and recharge them as needed. Most of what we know about battery issues comes from rumors or unverified speculation we see from time to time on the internet.

EV battery

Image courtesy Chevrolet

Until now. A company called GeoTab has created an EV Battery Degradation Tool to assess how battery life is impacted by 5 factors:

  • Time
  • High temperatures
  • Operating at high and low state of charge
  • High electric current
  • Usage (energy cycles)

After analyzing the battery health of 6,300 fleet and consumer EVs over 1.8 million days of operation, the GeoTab tool can now provide insight into how conditions in the real world influence the battery health of 21 electric car models from various manufacturers over a number of years.

“Battery degradation is a natural process that permanently reduces the amount of energy a battery can store, or the amount of power it can deliver. The batteries in EVs can generally deliver more power than the powertrain components can handle. As a result, power degradation is rarely observable in EVs and only the loss of the battery’s ability to store energy matters,” GeoTab says in an online post.

In developing the tool, GeoTab found that the the two biggest factors affecting the life of EV batteries are battery cooling and frequent high power DC charging. Age and number of miles driven are far less important to how long a battery lasts.

EV battery health chart

Image credit: GeoTab

Looking at the chart above, the average electric car battery will retain about 90% of its initial capacity after 6 years and 6 months of service. “Based on data from over 6,000 electric vehicles, spanning all the major makes and models, batteries are exhibiting high levels of sustained health. If the observed degradation rates are maintained, the vast majority of batteries will outlast the usable life of the vehicle,” the company says.

But individual models vary considerably. The battery in a Nissan LEAF, which does not have an active cooling system for its battery, will degrade twice as fast as the battery in a Tesla. “Good thermal management means better protection against degradation,” GeoTab says. But there are no simple answers. Differences in battery chemistry may have an effect as will the average ambient temperatures that any particular battery operates in over the course of its life.

For more information, go to GeoTab’s online tool to see the data that pertains to each individual model of electric car sold in the US. Want to know how a 2018 KIA Soul EV compares to the average? GeoTab knows, and that information is only a click away.

The data shows that batteries operated in hot climates deteriorate faster than those used in more moderate temperatures, but the most revealing finding has to do with how often the owner uses DC fast charging. Such chargers are becoming more popular as customers demand shorter and shorter charging times, but the effect they have on batteries may negate the benefit of the time saved. Take a look at the chart below.

GeoTab fast charging chart

Image credit: GeoTab

Tips To Preserve EV Battery Life

GeoTab offers these suggestions to maximize the life of your EV battery:

  • Avoid keeping your car sitting with a full or empty charge. Ideally, keep your SOC between 20-80% particularly when leaving it for longer periods, and only charge it fully for long distance trips.
  • Minimize fast charging (DCFC). Some high-use duty cycles will need a faster charge, but if your vehicle sits overnight, level 2 should be sufficient for the majority of your charging needs.
  • Climate is out of an operator’s control, but do what you can to avoid extreme hot temperatures, such as choosing shade when parked on hot days.
  • High-use is not a concern, so fleets shouldn’t hesitate to put them to work. An EV isn’t useful sitting idle in the fleet yard, and putting on more miles per vehicle is overall a better fleet management practice.

Drive Happy

The upshot of all this is that rapid battery degradation is not a significant issue for the vast majority of EV drivers. You can worry about it if you want, but on the overall scale of things that should concern you, it is about 437th on the list. If you have an electric car, drive it and be happy knowing you are leaving no carbon dioxide or particulates in your wake.

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Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new."


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