http://www.thedrive.com/news/3208/uc-irvine-accidentally-invents-a-battery-that-lasts-forever The UCI nanobattery endured 200,000 charge cycles over three months “with 94–96% average Coulombic efficiency.” It was effectively still brand new at the end of the experiment. via UC Irvine Accidentally Invents a Battery that Lasts Forever - The Drive.