Going to work is exactly why this system is pointless imo...... do you move a lot during work? I don't.. only to get coffee. It is simply as it is. Food to Energy conversion is terribly inefficient (which is really why the MATRIX trilogy is complete nonsense ;p).
And before you tell me that you enjoy exercise, you add 2kg to your weight, you need to spend the equivalent power to move that 2kg however you want it to. You are making a net-loss in energy to carry 2kg to charge a peace maker..
I am not talking about "does it work" because I know you can charge devices this way.. I am talking about that this is the absolutely most inefficient way to produce electricity there is. There is no worse way to generate electricity than this.
Biochemical electricity MIGHT work if we are implanted with a conversion unit that has high efficiency and requires LITERAL energy food bars for 90% or more efficiency. See Ghost in the Shell or Deus EX. But movement energy or heat energy conversion with a human being as platform??..... Yikes
I just don't see this as something I'd ever want. Give me a new battery that lasts 10 years and can be charged with bio-chemical conversion processes (fuel cells, essentially)....