What is EV battery degradation?

What is battery degradation?

EV battery degradation is the decline in a battery's capacity and efficiency due to chemical and physical changes within the battery cells over time. This results in a reduced driving range and diminished performance, impacting the overall utility and longevity of the vehicle.

How much do EV batteries degrade?

Well, it depends! Generally EV batteries are pretty durable and all come with a warranty of at least 80,000 miles or 10 years – whichever is first. On average though, we see that degradation is only a couple of percentage points per year. However, it can be much more than this, depending on how the vehicle has been used and some natural variation from the factory.

In the below data from a sample of around 200 EVs we tested, you can see that there is a fair amount of variation!

What are the causes of battery degradation?

Firstly, it's worth knowing that EV batteries degrade over time whether you use the car or not. It can't be completely avoided, but it can be significantly reduced.

Several factors contribute to the degradation of EV batteries. Understanding these factors can help owners take proactive measures to minimise their impact:

• Storing at high charge levels: Keeping the battery at 100% charge for extended periods will cause the battery to degrade faster than one kept at lower states of charge.

• General driving style: Being hard on the accelerator and driving aggressively will cause increased thermal and mechanical stress

• Frequent rapid charging: While sometimes necessary, rapid charging generates more heat and can stress the battery, leading to quicker degradation.

• Deep discharges: Allowing the battery to frequently drop from very high to very low levels before recharging can cause wear and tear over time.

Why does it matter?

An EV battery is typically considered not usable anymore when its capacity degrades to around 70-80% of its original capacity. Replacing a battery is a significant cost, as the battery generally represents 40-50% of the value of the vehicle when new.

As well as the risk of replacement, the key impacts of degradation are:

• Range reduction: As the battery capacity degrades, the vehicle's range decreases proportionally. When the range reduction becomes significant enough to impact the vehicle's usability for its intended purpose, the battery may be considered at end-of-life.

• Performance decline: In addition to capacity fade, power fade can occur, affecting acceleration and regenerative braking efficiency. When these performance issues become noticeable, it may indicate the battery is nearing the end of its useful life.

• Charging efficiency: As batteries age, they may take longer to charge and may not hold a charge as well. This can make the vehicle less practical for daily use.

• Safety concerns: In rare cases, severely degraded batteries may pose safety risks.

Conclusions

Maintaining good battery health is crucial for the overall performance and longevity of your electric vehicle. We recommend:

• Test batteries before buying: Before you buy an electric vehicle, it is worth having a Generational battery health test. Even if a battery is within the manufacturer's warranty, a car with an 85% SoH is going to have significantly reduced performance compared to

• Understand degradation and plan: By understanding the factors that cause battery degradation and with a little bit of planning, EV owners can ensure their vehicles retain their performance (and value) for a really long time.
  

A well-maintained battery not only provides a reliable range but also contributes to a prolonged lifespan and a higher resale value for the vehicle.