This is a very burning issue, and I think many engineers have been working on how to generate energy that wearable can use without fixing battery in them. The question is then, how do we trap such energy? We can use the environment temperature with respect to that of the body or the energy can be trapped following the physical movement of an individual. What we should know is that, this will not be that simple interns of its effectiveness, for one reason that there will be no constant energy flow and all the circumstances.
No reason why movement/kinetic energy cannot replace a battery, or keep a battery or supercap charged. Your point is valid, I was agreeing with you. But also pointing out that such energy harvesting is a proven technology that has been used for a long time and therefore would most certainly be viable in today's applications.
Very good point @_hm...but how do we tap to the energu we consume via food?...I remember readng about glucose harvesters, but by definition they need to get implanted somewhere in your body and get the energy out from there, not a pleasant solution even if it works...the most simple is to tap to the temperature difference between the body and environment but this only works in cold climate or air conditioned rooms...Kris