How much will my EV battery degrade over time, and what contributes to degradation

Tesla battery charging

One of the biggest concerns for people considering the purchase of a Tesla or any battery electric vehicle (BEV) is how fast the battery will degrade, and if they’ll have to replace the battery during the time they own the car.

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While no one has the perfect answer for these questions, a fleet-telematics company Geotab has attempted to answer it using data from BEV fleet operators from around the world.

Let’s start off with the good news. EV batteries last longer than most people expect, and most will outlast the usable life of the vehicle itself. On average, they found that EV batteries lose about 2.3% per year.

Tesla battery degradation over time

One of the fleet operators that contributed data to the study was Tesloop, a Tesla rental service in southern California. They have a Tesla Model X which recently passed the 330,000 mile (531,000km), and its range dropped from 260 miles to 200 miles (418km to 321km), or about 23%.

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So what makes EV batteries degrade faster over time?

Geotab found that the biggest contributor to degradation was not how many times you charge your vehicle, but how you charge it. Frequent fast-charging has a greater impact on battery life than slower Level 1 or Level 2 charging. The other leading factor was temperature – warmer climates led to faster battery degradation.

When these two factors are combined they found that after six years, EV batteries lost about 10% of their original capacity.

Which automakers batteries fare the best over time?

Geotab also found in their analysis that not all batteries from the EV automakers fare the same over time, with some degrading, on average, faster than others.

They compared a 2015 Tesla Model S against a 2015 Nissan Leaf. The Leaf suffered from an average degradation rate of 4.2% over 4 years, while the Model S only had a 2.3% degradation over the same time period.

Tesla Model S vs Nissan Leaf battery degradation

What is the difference between the two that would cause the Leaf to degrade twice as fast as the Model S? The Tesla has a superior thermal management system in place that uses liquid to cool the battery, as opposed to air cooling with the Nissan.

How to extend the life of your battery

To maintain battery health and reduce degradation, Geotab suggests the ideal state of charge (SOC) is between 20%-80% and to reduce fast-charging as much as possible. They also suggest keeping the battery cooler (i.e., those in cooler climates) will help extend the life, good news for Canadians.

Finally, don’t be afraid to drive your EV. Geotab found that high use did not correlate to an increase in battery degradation. That has been supported by several high mileage Tesla’s, like this Model S that recently passed 1,000,000km.

You can compare the degradation over time of all Tesla models against other vehicles used in the study by using Geotab’s comparison tool.

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Founder and Editor-in-chief of Drive Tesla Canada | Darryn@DriveTeslaCanada.ca Have a Tesla tip? Email tips@driveteslacanada.ca, or DM us on Twitter @DriveTeslaca