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"  Long-term owners of laptops, smartphones, and other things powered by lithium-ion batteries are all too familiar with one quality of the world&amp;#039;s leading power-storage technology: eventually Li-ion batteries lose their charge. And eventually that same fate will creep into electric vehicles.  Take Tesla&amp;#039;s first car, the Roadster. Back in 2006, Elon Musk&amp;#039;s automotive venture estimated that after five years of driving (averaging 10,000 miles per year), the charging capacity of the Roadster&amp;#039;s battery pack would drop to 70 percent of its original capacity\u2014leaving owners with an ever-shrinking range. But based on a study released late last week, Tesla&amp;#039;s life-expectancy projections for the Roadster&amp;#039;s battery pack appear to be on the conservative side. After analyzing anonymous charging data from 122 Roadsters\u2014accounting for roughly five percent of the current road-going fleet\u2014non-profit EV advocacy group Plug In America concluded that Roadster batteries should retain between 80 to 85 percent of their original capacity after 100,000 miles. The study encompasses more than three million cumulative miles driven, with roughly 25,000 miles on the odometer of the average Roadster (and in one case, more than 87,000). It found that the Roadster&amp;#039;s battery backs are losing on average 3.7 &amp;quot;ideal miles of range&amp;quot; (Tesla&amp;#039;s proprietary battery-capacity measurement unit) every 10,000 miles. Plug in America conducted a similar study examining the Nissan Leaf, and saw similar degradation patterns. The difference between the two cars seems to be that with the Roadster, unlike the Leaf, researchers saw &amp;quot;no significant correlation between climate and battery pack longevity.&amp;quot; Although Tesla fans might be quick to point out the California-based automaker is producing the industry&amp;#039;s best batteries, the study found that there wasn&amp;#039;t enough variation in the climate data in its study of the Roadster, &amp;quot;so it&amp;#039;s possible an effect from climate will emerge as more data is collected.&amp;quot; But what about the Model S? Plug-in America says it is still evaluating the company&amp;#039;s latest EV, which is currently backed by a 8-year, 125,000-mile warranty for the 60 kWH battery pack, and a 8-year unlimited-mile warranty on the 85 kWh one. But don&amp;#039;t expect anything conclusive for a while: The Model S has been on the road for just over a year, so any meaningful evaluation of its battery health will have to wait until the end of the decade. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/cars/a9271/tesla-roadster-batteries-aging-well-15701200/>