Low Battery?

Now if your cell phone battery runs down, just walk around the block and power it with your steps. Okay, so the real early applications will likely be for people with medical needs, like insulin pumps and neuroprosthetic devices as those are developed. But, eventually, I want one. I saw this blurb in online Science Magazine info:

"As we walk, we expend energy not only in pushing off with our planted leg, but also when our other leg decelerates as it makes contact with the ground -- energy that could be harvested for other uses, according to a new study. In a Report in the 8 Feb 2008 Science, Donelan et al. described the development of a knee-mounted mechanical device that can covert the expended mechanical energy of the deceleration step of walking into electrical power. The so-called "biomechanical energy harvester" consists of an aluminum chassis and generator mounted on a customized orthopedic knee brace, and weighs about 1.5 kg. Embedded sensors detect the angle and velocity of the wearer’s leg, switching the device on only during the braking phase of each swing -- analogous to regenerative braking in hybrid cars, where energy normally dissipated during braking drives a generator instead. The team reported that volunteers walking with one device on each leg produced an average of 5 watts of electricity -- enough to power 10 cell phones. The ability to produce substantial electricity with little effort makes this technology attractive for powering prosthetic limbs or other portable medical devices. A related ScienceNOW story by D. Powell highlighted the innovation."