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Nissan Suggests Leaf Battery-Capacity Loss Due To High Miles: Exclusive

It's been a few months now since reports of losses in battery capacity in Nissan Leaf electric cars began to filter out of Arizona.

Owners have complained to Nissan's Consumer Affairs group and written hundreds of posts on owner forums. In July, Nissan Americas took seven different Leafs in for a complete assessment by the technical unit at its Arizona Testing Center.

Now Nissan is starting to reveal the conclusions it's drawn from examining those seven Leafs and their battery packs.

Mark Perry, Nissan North America’s product planning and advanced technology director, discussed the company's findings exclusively with Green Car Reports.

19,000 miles or more

The common thread among the seven Leafs from Arizona, Perry said, was that all of them had covered much higher mileage than the 12,500 miles Nissan used to estimate the rate of battery capacity loss over time.

All of them had covered at least 50 percent more than that--or roughly 19,000 miles a year--and a few were "significantly higher" than that.

[UPDATE: After this article was published, Nissan used the actual mileage of the seven cars in the test to provide additional data. "The average mileage for the cars investigated was 19,600 miles, and the average in-service time was 14.7 months," wrote the company's Katherine Zachary. "Average annual mileage [of those cars] is about 16,000 per year, more than double the average Phoenix customer mileage of 7,500 miles per year."]

As a sprawling suburban city, Phoenix also requires a higher proportion of travel at freeway speeds, with relatively less time spent in low-speed urban stop-and-go traffic.

Based on those factors, Perry said, "The cars and the battery packs are behaving as we expected" given the use they've logged to date.

Starting in 2009, Nissan executives have consistently said the Leaf battery pack would retain 70 to 80 percent of its charge capacity after five years--and average roughly 70 percent capacity after 10 years.

In other words, capacity loss is not linear, but quicker during the first few years than in subsequent years, assuming equivalent mileage in every year.

Assuming averages

Those projections, based on battery testing during development of the Leaf, assume the car covers 12,500 miles a year, in climates largely similar to those of Los Angeles (50 to 90 degrees F, with an average temperature of 68 or 70 degrees).

Phoenix has also just had one of its hottest summers ever, he noted.

Looking at 450 Nissan Leafs now in Arizona, Perry said, using data each car transmits to a Nissan control center, it appears that Leafs in Arizona are "on a glide path" to average battery capacity of 76 percent after five years rather than 80 percent.

The seven cars the company inspected in depth are likely to have less capacity than that after the same time.

Perry said he couldn't comment on what the company's data showed regarding frequency of charging and frequency of quick-charging for the Leafs it inspected.