Cellphone battery running low? Just go for a walk and charge it up.

Shoe leather as a renewable resource: Penn biologists invent power-generating backpack:

PHILADELPHIA – If you already have a little spring in your step, a team of biologists at the University of Pennsylvania would like to them to good use by adding a few more springs in the form of a power-generating backpack. Details of their prototype "Suspended-load Backpack" were announced today in the journal Science. The device converts mechanical energy from walking into electricity – up to 7.4 Watts – more than enough energy to power a number of portable electronic devices at once...