Fast charging is not a friend of electric car batteries

EV batteries are lasting longer than many expected.
EV batteries are lasting longer than many expected.
Image: REUTERS/Bobby Yip
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Every year, electric car batteries degrade. How much depends on factors only now being tested in the real world.

Some of the best data come from informal trials of electric vehicles (EVs) being conducted by fleet operators around the world. A detailed looked was supplied this week by the fleet-telematics company Geotab. It plumbed data from 6,300 fleet and consumer EVs to understand how their batteries were faring in the real world. It was a mixed bag.

The good news was that batteries last longer than many expected. On average, EV batteries lose about 2.3% per year—or 23 miles for an EV with a 200-mile range over five years. Geotab suggests at that rate most batteries will outlast the useable life of their vehicles (fleet owners often auction off their vehicles after 100,000 miles). Or it may change how long fleet owners retain their vehicles.

A Tesla rental service in Southern California, Tesloop, has driven its vehicles well beyond 300,000 miles, with no plans to remove them from service. One Model X, after covering 330,000 miles, saw its original battery’s range fall from 260 miles to 200 miles (23%)—for comparison, pooled data from Tesla owners shows batteries losing about 10% of their charge after 155,000 miles.

But not all brands performed the same: The Nissan Leaf’s passive air-cooled batteries were bested by Tesla’s liquid-cooled versions, suggesting thermal management is a key differentiator for carmakers. You can compare brands with Geotab’s tool here.

What affects EV battery health?

Surprisingly, heavy use (charging many times per week) did not meaningfully accelerate EV battery degradation. But heat and direct current did. Batteries lost their capacity faster in warm climates. Frequent fast-charging (direct current) also took a toll compared to slower Level 1 or 2 charging (alternating current at 120 and 240 volts). Combined, the two factors led to faster battery degradation: about 10% of the original capacity after six years.

Geotab added a few caveats. Degradation is not linear. A slow decline for many years can be followed by a steeper drop. None of the vehicles studied had reached that point, so more analysis will be needed to understand the full EV battery lifecycle. Tesla owners also mentioned that range is not the only factor: how fast it charges may change over time, particularly as carmakers introduced over-the-air software updates designed to protect batteries even if it negatively affects capacity and charging times. As always, correlation is not causation: It’s possible other factors associated with hotter climates (not just heat) may play a role in battery degradation.

Overall, Geotab recommended keeping EVs charged between 20% to 80%, minimizing fast charging, and sticking to temperatures on the cooler side if possible as the ideal way to extend the capacity of your EV battery. As the first generation of mass-produced EVs approaches a decade or more on the road, we’ll soon have far more data about how well they age.