DC Fast Charging, Passive Air Cooling Systems Lead to Quicker EV Battery Degradation

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【Summary】There are multiple common factors that impact the longevity of a lithium-ion battery, but high temperatures and high electric currents are the two that have the greatest impact.

Original Vineeth Joel Patel    Jan 28, 2020 5:30 AM PT
DC Fast Charging, Passive Air Cooling Systems Lead to Quicker EV Battery Degradation

Electric vehicles may require less maintenance and care than vehicles with internal combustion engines, but that doesn't mean their immune to having components that wear out over time. Lithium-ion batteries aren't engineered to last forever and need to be replaced, eventually. 

With automakers choosing different battery components and using different chemicals to manufacture batteries, it can be difficult for consumers to have a good idea of how long their electric car's batteries should last. Fleet management company Geotab conducted research on 6,300 electric vehicles with the aim of trying to see how long a battery should last.

Five Factors To Keep An Eye On

The company's findings revealed five common factors that can impact the health of a lithium-ion battery: time, high temperatures, operating at high and low state of charge, high electric current, and usage (energy cycles). All of these things can lead to battery degradation, a process that results in a decrease in how much energy a battery can store or the amount of power it can deliver, claims Geotab.

The company's findings portray modern lithium-ion batteries in a good light. After Geotab concluded its tests, it claimed that the majority of EVs come with batteries that should outlive the life of the vehicle. 

With that being said, the average degradation across all EVs was roughly 2.3 percent a year. To put that into perspective, an EV with a 150-mile range will lose approximately 17 miles a range after five years. That's not a negligible amount, but it would go noticed by a lot of owners.

Beyond the average amount of battery degradation, Geotab found two major things that impacted the overall lifespan of a battery: cooling and DC fast charging. Temperature control techniques, or the way an automaker decides to keep batteries cool in an EV, had a dramatic effect on how long they lasted. There are two major ways automakers keep batteries cool in electric cars: air and liquid. Cooling systems that were liquid cooled had less degradation.

Drastic Differences Between Automakers

Comparing a Tesla Model S to a Nissan Leaf painted the picture of how cooling affects degradation. The Leaf has a passive air cooling system to keep its batteries at an optimal temperature and its average degradation was at 4.2 percent. 

Tesla uses a liquid cooling system and its average degradation for the Model S was 2.3 percent. As Geotab puts it, "good thermal management means better protection against degradation."

The other major thing that impacted battery longevity was DC fast charging. While a lot of owners will use Level 1 or Level 2 charging for the most part, automakers have started to incorporate DC fast charging capability for their EVs, as the aforementioned ways of charging can take hours. 

Unfortunately, Geotab found that EVs that are charged on DC fast chargers one to three times per month had batteries that degraded much quicker than if they hadn't been hooked up to a fast charger. Using a DC fast charger more than three times a month further accelerated the degradation. The company cautions owners to not use DC fast chargers often and to prioritize Level 2 chargers for longevity.

Owners looking to maximize the lifespan of their batteries should follow these tips.

- Avoid letting your EV sit with either a full or empty charge. If you plan on keeping your EV sitting for an extended period of time, try to keep the charge somewhere between 20 and 80 percent.

- Use DC fast charging as little as possible.

- Try not to operate your EV in extremely hot temperatures. If you can't avoid harsh weather, try to find a shady spot to park the vehicle.

If you're still worried about battery degradation, Geotab has a helpful tool where you can compare EV degradation against competitors.

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