One of the last times we saw the concept of a self-recharging battery, it was part of a high-minded Nokia patent whose ideas still haven't seen the light of day. Researchers at Georgia Tech are more inclined to put theory into practice. Starting from a regular lithium-ion coin battery, the team has replaced the usual divider between electrodes with a polyvinylidene difluoride film whose piezoelectric nature produces a charging action inside that gap through just a little pressure, with no outside voltage required to make the magic happen. The developers have even thumbed their noses at skeptics by very literally walking the walk -- slipping the test battery under a shoe sole gives it a proper dose of energy with every footstep. At this stage, the challenge mostly involves ramping up the maximum power through upgrades such as more squeezable piezoelectrics. Georgia Tech hasn't progressed so far as to have production plans in mind; it's nonetheless close enough that we could see future forms of wearable computing that rarely need an electrical pick-me-up.