Replacing EV Batteries: Your Costs Will Vary

By · June 19, 2012

Nissan Leaf

There are questions about the life of the LEAF's 24-kilowatt-hour battery pack. (Jim Motavalli photo)

Yes, electric cars are selling slowly, and one central reason for that is consumers' fear that the battery packs won’t last, and then will cost a fortune to replace—or dramatically lower the value of the car. Is that a false fear? I’d love to be able to dispel the whole question right here and now, but there simply isn’t enough information to do that with confidence.

The questions need to be addressed, because battery replacement costs is one of three key considerations why 57 percent of Americans cited in a USA Today/Gallup Poll say they wouldn’t buy an EV. The other two are range per charge and recharge time, both things that will probably get satisfactorily addressed before battery replacement cost is laid to rest as a concern. (The poll might have been more objective if it hadn’t defined an EV as “an electric car that you could only drive for a limited number of miles at one time.”)

First Battery Wear

Some owners have already put 30,000 to 40,000 miles on their LEAFs, and we’re getting the first reports of battery power loss. The LEAF has a 12-bar indicator and Nissan says it’s seen the loss of a bar in “a few cases.” Mike Ferry, the transportation programs manager at the California Center for Sustainable Energy, says he’s seen it in exactly one LEAF (with 40,000 miles on it).

Leaf bars

Fast charging may turn out to be a factor in battery life. Total capacity of the battery even when fully charged can be reduced.

Nissan just opined that its LEAF battery pack will have 80 percent charge left after five years, and 70 percent after 10 years. That’s fine, but when does the pack become a boat anchor? To be fair, these packs will probably never get thrown unceremoniously into a landfill. The lithium in them can be reused, and as John O’Dell writes at Edmunds.com, EV batteries are 70 to 100 percent recyclable, and companies such as Umicore and Toxco are already gearing up to handle the recovery of their valuable metals. The catch is that lithium isn’t very valuable now, about $30 per pound, but that should change as volumes increase and demand for it grows.

Brett Williams, a senior researcher in electric drive energy at the University of California, Berkeley, told me that EV packs are likely to have 70 to 80 percent of storage capacity left when they’re ready to be retired from auto use. O’Dell agrees with that figure. “Conventional wisdom,” he said, “is that remaining life of around 75 percent to 80 percent renders them not useful for automotive, but still plenty useful for stationary storage.” OK, so then when the car is just five years old it will need a complete new battery pack? Not so fast.

Replacing Cells, Not Packs

Simon Sproule, a Nissan vice president, says that it’s unlikely that whole LEAF packs will need to be replaced when the magic 75 to 80 percent threshold is reached. Instead, he said, EV medics can find bad cells and replace them, at a cost of hundreds of dollars, not thousands. I hadn’t heard that before, but LEAF salesman Paul Scott tells me that it’s possible to “replace certain underperforming cells rather than the whole pack.”

Ferry says that not all packs are designed for the replacement of individual cells or modules, though the LEAF pack definitely is. Omo Velev of AeroVironment, who consults with the California Center, said that EV packs are designed to maintain even degradation across all cells, but in practice some go bad faster than others. If enough of them do that, the utility of the while pack is compromised.

Cells can go bad, Velev said, through:

* Very small changes in cell chemistry and “micro-impurities” that compromise life;

* Mechanical imperfections, due to poor seals, loss of electrolyte or other factors;

* Environmental conditions related to the cell’s position in the car, resulting in significant differences in temperature and vibration. If it’s individual cells going bad, Velev said they can be replaced, allowing the whole unit to be “rejuvenated” to an approximation of its output when new.

Also, certain lithium chemistries, including iron phosphate, degrade in a linear fashion. In other words, the lights on the battery health indicator will go out in evenly spaced intervals. But the lithium manganate in the LEAF is less linear. A Nissan rep told Green Car Reports that its battery is non-linear, losing—like many other packs—more capacity early in life. “The curve flattens over time,” Nissan said.

A Second Life

Meanwhile, experiments in using batteries for utility back-up duty are ongoing. Ferry says that its four-bay EV battery test station at the University of California, San Diego is putting two A123 and one Enerdel pack through its paces, and that they’re producing approximately 120 kilowatts of power that’s being absorbed into UCSD’s microgrid.

According to Ferry, the tested packs are several years old, but haven’t been through many cycles yet. “It will get interesting when the packs reach the age you’d expect them to have when they’re pulled out of a car,” he said. EV packs can supply backup power to the grid, but Ferry said that’s un-critical duty that under-stresses the packs and could be performed by lead-acid. Alternative duty includes grid functions like frequency regulation and voltage support, and that’s taxing and might lead to shorter battery shelf life. But getting that kind of information is what the UCSD test is all about.

And how much will the LEAF pack cost to replace, if the whole thing does go bad? We’ve seen company cost estimates of between $9,000 and $18,000, but that’s for very early packs. Technical improvements and economies of scale should bring that down.

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