My cell phone generally runs out of juice after three hours when the GPS is actively in use, which is the scenario when I’m tracking my bike rides. Engineers Aaron Latzke & David Delcourt in San Francisco designed this clever USB charging system that inserts over your bicycle rear wheel axle between the fork and the hub. It looks like they’ve thought of everything.
(At first I freaked out when I saw that women using her Kryptonite New York Lock on the top tube but then I noticed the locking skewer for her wheels, so she’s good.)
If my math is correct and the claims from Siva are accurate, it looks like this Siva Cycle Atom USB charger pulls a hair over 3 watts of power from my legs. I think I can sacrifice 1½% of my cycling effort on a long ride to keeping my phone charged.