Power is one of the big challenges in Wearable Computing.

Via Technology Trends there is a report about the worlds smallest battery that is also implantable. It could be used in a forthcoming version of the Army's Power Vest. I mean I would'nt join the army to get this battery. I would even never implant a battery though. But if i would have Parkinson's disease or muscular impairments I would use it.

How it works sounds like SciFi but it is already in the phase for production partner search: "These microstimulator systems would be implanted near nerves, where they emit electrical micropulses that stimulate nearby muscles and nerves."