The Stromer ST1 X is powered by a 618 Wh lithium ion battery, which sits inside the bike's down tube, and it has the potential to drive the bike's 500W rear hub motor at speeds of up to 28 mph for a range of up to 70 miles per 5 - hour charge (or up to 90 miles of range with an optional 814 Wh battery). (treehugger.com)