The truth about battery degradation in electric vehicles

The truth about battery degradation in electric vehicles

By Mike Nakrani, CEO

There’s a lot of noise around battery degradation, and battery technology as a whole. So, I thought it would be useful to provide some high-level thoughts on the former (with plans to write about the technology itself in a future post).

The prevailing perception is that electric vehicle (EV) batteries degrade over time, and there are various reports out there that suggest lithium-Ion batteries degrade at a rate of around 2.3% each year.

If this is true, then over a period of 20 years (or 200,000 miles), we might expect an electric battery to degrade by around 46%. The rule of thumb that many people use, is that if the battery falls below 70% of its original capacity, then it’s no longer fit for purpose and should be replaced.

However, in my view, the reality is that the latest EV batteries are likely to last much longer. I was one of the early adopters and still own a 2013 Chevrolet Volt. The car is classified as a range extender vehicle, i.e., it ran on battery power and was charged by a small gasoline engine when it run out.

Of course, this is early battery technology, so the range is around 50 miles. However, living in the city means I have fairly low mileage, so I charge the vehicle every night at home in the driveway.

After 10 years and 52,000 miles, I’m pleased to report that the vehicle is still going strong, and I can see no discernible deterioration in battery performance. I know this is anecdotal, and a sample size of 1, so I wanted to highlight some more thorough research from Tesla…

In April of this year, Tesla released its latest Impact Report, announcing that battery degradation in its Model S and Model X vehicles is only 12% after 200,000 miles. Now that’s pretty remarkable, and given that larger batteries degrade more slowly, fleet operators that use trucks and buses have reason to be confident that EVs will be cost-efficient over the long-term.

Why electric batteries degrade

The main reason that EV batteries degrade is that they use lithium-ion cells, which start depleting as soon as they’re created. Additionally, as an electric battery goes through charge cycles, it slowly loses its maximum potential, which is known as cycling ageing.

The lifetime capacity of a battery is referred to as its state of health (SoH). Brand new batteries have a 100% SoH, which inevitably reduces over time. When an EV battery falls to a 70% SoH, it’s considered to be at the end of its life.

Whereas most EV manufacturers expect batteries to last between 10 and 15 years, as we see in Tesla’s latest report, advances in technology mean that the latest batteries have the potential to last much longer – especially if they’re larger in size.

The role of EV battery warranties

The fact is that some EV batteries will last longer than others. However, even if a battery degrades quicker than expected, fleet operators are covered under a warranty.

Every EV manufacturer offers a separate battery warranty in addition to its usual vehicle coverage. Most offer an eight-year/100,000-mile warranty and will either restore or replace batteries if their SoH falls below 70%.

For example, Tesla’s Model X and Model S vehicles are covered by the company’s Battery and Drive Unit Limited Warranty, which uses these terms with additional exclusions and limitations.

How fleet operators can minimise EV battery degradation

Despite being covered by a warranty, prevention is still better than cure.

Battery degradation can be minimised by ensuring vehicles are charged only when they need to be. Continuous charging puts unnecessary strain on batteries and degrades them quicker.

Likewise, it’s best to avoid letting an EV battery go completely flat. It’s recommended that they should be charged to 20-80% capacity for optimum longevity.

Our fleet management dashboard, VEV-IQ, enables fleet managers to automatically track vehicle performance, energy use and charging behaviours to ensure fleets run at maximum efficiency.

Closing thoughts

According to the Department of Energy, the cost of an EV battery in 2022 was $153/kW – 90% lower than in 2008.

As EV batteries become more affordable to manufacture, companies will start developing larger batteries that last longer.

Similarly, as lithium-ion technology improves, degradation rates will become slower, improving EV battery lifespans even further.

Get in touch with one of our expert team and find out more about VEV’s commitment to fleet electrification.

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