Even As Batteries Age, Electric Cars Meet Commuter Needs: Study

April 14, 2015

As the modern lithium-ion and lithium-polymer batteries in our smartphones and personal electronics age, the more often we have to plug them back in to keep them charged and useful—and the less likely they are to make it through a day when we ask a little more from them.

We’re probably all too familiar with that pattern and, unfortunately, the same goes for electric cars, which can lose 20 percent or more of their range over a few years daily use.

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Factor in so-called “range anxiety”—the concern that you might not have enough driving range to reach your destination or next charging point—and that dwindling range as the battery ages may be cause for some electric-car shoppers to either worry about budgeting for a replacement battery pack or forget about it and go with a hybrid instead.

While it’s a valid concern for the few who are really pushing the range of their vehicles on a daily basis, researchers at the Department of Energy’s Lawrence Berkeley National Laboratory have examined how soon electric-car batteries lose usefulness—and the findings are quite surprising.

2011 Nissan Leaf owned by Nikki Gordon-Bloomfield

2011 Nissan Leaf owned by Nikki Gordon-Bloomfield

Still good enough for 80 percent of households, even with half of driving range lost

To start, they note that even if their test Nissan Leaf EVs were to lose 20 percent of their capacity (officially 24 kWh, with an EPA driving range of 84 miles)—as the Leaf’s instrument cluster drops bars from its instrument cluster to show—they can still meet the daily-driving needs of 85 percent of U.S. motorists. Even at 50 percent of its original storage capacity, about 80 percent of daily driving needs could still be met, the researchers calculated; and at 30 percent of the original, 55 percent would still have enough.

That’s quite different than the 70 percent of original capacity that’s often considered the end of life for electric-vehicle batteries.

Those daily-driving needs weren’t just calculated using average miles traveled, but with various driving simulation patterns that included partial charges, mixes of city and highway driving, and hilly terrain. And those patterns were based on nearly 160,000 actual daily driving itineraries from the DoT’s National Household Travel Survey.

“It is important to remember that the vast majority of people don’t drive more than 40 miles per day on most days, and so they have plenty of reserve available to accommodate their normal daily trips even if they lose substantial amounts of battery capacity due to degradation,” said Dr. Samveg Saxena, who co-authored the report and heads the vehicle powertrain research program at Berkeley Lab.

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Power fade also not an issue

The researchers also tested performance of the Leaf models after their batteries were beyond their originally intended life. Even as capacity is significantly down from its original level, it can still deliver the power needed for acceleration and performance close to the level of when it was new.

“In sum, we can lose a lot of storage and power capability in a vehicle like a Leaf and still meet the needs of drivers,” Saxena said.

This is an important note, as the Nissan Leaf, as well as a few other electric shorter-range electric models like the Mitsubishi i-MiEV, are moving into the used-car market. There's no need to dismiss used models with some lost range as defective, non-functional, or non-viable.

If you’re considering a heavily used Leaf or other EV as a second or third car, and it’s lost quite a bit of its range, don't necessarily rush to replace the battery pack; it could still be quite useful for years to come as a daily commuter.

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