8 lessons about EV battery health from 6,300 electric cars

A persistent concern among some EV drivers is the long-term health of the battery. All batteries lose some storage capacity over time. But how might that degradation affect your driving range a few years down the line? To help answer that question, we can now look to Geotab, a leading telematics-fleet-management company with access to a lot of EVs. Lo and behold, the losses are minor.

Geotab created its so-called EV Battery Degradation Tool by pulling data directly from the 6,300 EVs from its fleets. What’s super-cool is the interactive nature of the tool, allowing users to drill down to 21 specific electric models.

You can use the tool to slice and dice the data for yourself.

In June 2018, Geotab acquired FleetCarma, a forerunner in providing technology support the use of EVs in fleets.

Here’s a quick rundown of what the data revealed:

• If current degradation rates are maintained, the vast majority of batteries will outlast the usable life of the vehicle.
• The average decline in energy storage is 2.3% per year. For a 150-mile EV, you’re likely to lose 17 miles of accessible range after five years.
• EV batteries decline in a non-linear fashion. There’s an early drop, but the rate of decline slows down in subsequent years.
• Liquid-cooled batteries decline slower than air-cooled packs. Geotab saw that a 2015 Tesla Model S with liquid cooling had an average annual degradation rate of 2.3%, compared to an air-cooled 2015 Nissan Leaf’s rate of 4.2%.
• Battery-powered vehicles that have bigger state-of-charge buffers fare better. In other words, some carmakers use a smaller percentage of the battery’s capacity, which reduces usable range. But the conservative approach slows down the degradation rate, most notably in early versions of the Chevrolet Volt plug-in hybrid.
• Higher vehicle use does not necessarily equal higher battery degradation.
• Vehicles driven in hot temperatures show a faster decline in battery health.
• The use of DC fast-chargers speeds up the process of degradation, but there’s not much difference in battery health based on frequent use of Level 1 versus Leve 2 charging. Losses that happen with frequent DC charging are made worse in hot climates.

How much degradation over time have you experienced with your EV?