Battery capacity degradation is to be expected with any battery-powered electric vehicle. The questions are how much degradation, how fast, and what is covered under the warranty. GM released the owner’s manual for the Chevy Bolt EV this week and in it, the automaker warns of potential battery degradation of up to 40% during the 8-year warranty period or within 100,000 miles.

GM wrote in the manual (PDF – page 322 first spotted by GreenCarReports):

Like all batteries, the amount of energy that the high voltage “propulsion” battery can store will decrease with time and miles driven. Depending on use, the battery may degrade as little as 10% to as much as 40% of capacity over the warranty period. If there are questions pertaining to battery capacity, a dealer service technician could determine if the vehicle is within parameters.”

10 to 20 percent within 8 years or 100,000 miles would be expected, but 20 to 40 percent could be problematic. We are talking about losing up to 95 miles of range out of the Chevy Bolt EV’s 238-miles range. But that’s not what GM says you should expect. It’s what is covered by the warranty.

For comparison, Tesla warns that it does not cover battery degradation from “battery usage” under its warranty:

“The Battery, like all lithium-ion batteries, will experience gradual energy or power loss with time and use. Loss of Battery energy or power over time or due to or resulting from Battery usage, is NOT covered under this Battery Limited Warranty. See your owner documentation for important information on how to maximize the life and capacity of the Battery.”

Of course, it covers any defect on the battery, including if the defect results in abnormal capacity losses, but it doesn’t really define a normal capacity loss. Early data shows a trend of reaching 150,000 miles before coming close to a 10% capacity loss, which is the minimum loss expected by GM under its warranty. Tesla’s battery and drivetrain warranty is for 8-year and with unlimited mileage.

It’s too soon to have the data for the Bolt EV, but hopefully, it follows a similar trend as Tesla’s battery degradation and not what the warranty is covering.

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