Nissan's Andy Palmer explains Leaf battery capacity loss to Chelsea Sexton
The last few months has seen Nissan facing a growing controversy where Leaf owners are reporting a more-rapid-than-expected loss of battery pack capacity. The controversy included a massive test conducted, in Phoenix, independently by Nissan Leaf owners that verified several Leaf's which have a higher-than-expected loss of battery pack capacity. Nissan is working with EV Advocate Chelsea Sexton to form an independent Advisory Board meant as a venue for Leaf owners to help Nissan understand Leaf owner concerns and help Nissan's marketing with communication issues. As a companion to announcing details of the Advisory Board, Nissan published a video interview between Chelsea Sexton and Nissan Executive Vice President Andy Palmer concerning the Leaf battery capacity loss controversy and other issues.
The tone of the interview is somewhat impersonal, as if Nissan wants to project an image of openness.
Battery pack capacity loss issue in Arizona: Saying "lets be straightforward" Palmer says "there is a degradation of a battery over [its] life" and that the degree of degradation over time is a clear matter of physics and chemistry.
The most important thing Palmer says is that the degradation curve is non-linear, or that it does not degrade by the exact same amount each year. The Nissan Leaf owners seem to be expecting a linear degradation of battery pack capacity. Instead there is an initial rapid loss of capacity, and that the rate of capacity loss tapers off over time. This is implied by the shape of the curve Palmer draws in the air with his fingers. This is also implied by saying that after 5 years there will be 80% remaining capacity, and after 10 years 70% remaining capacity, meaning that the rate of degradation is less as the battery pack ages.
The "non-linear" rate of capacity loss is an example of a detail that Nissan did not communicate to Leaf owners.
The four "main" variables for the degradation rate Palmer describes are: "Speed and gradient" the car is driven, meaning that frequent drives at highway speed is bad for the Nissan Leaf battery life, as would be frequent drives in the mountains. "Continuous or very frequent fast charging" will degrade the battery pack, and Nissan recommends at most one fast charge per day. However, this is a direct contradiction of a statement by Mark Perry last spring. He clearly said the Leaf was designed with fast charging in mind, "on a daily basis, 2-3 times a day, with no damage to the battery." "The mileage of the vehicle" or how many total miles it is driven per year. "Temperature, cold and hot" also affect the rate of degradation. Based on the average of Phoenix Leaf owners, who drive on average 7,500 miles/year, in a hot climate, that encourages/requires frequent highway speed driving, Nissan expects that after 5 years in the hands of an average Phoenix Leaf owner, the battery pack will have degraded to 76% remaining capacity. This is is a faster degradation than in other climates.