They’re powered by your movement, not by your metabolism.
But for my electricity, I use only the finest hand crafted artisanal electrons. They work much better than your factory farmed electrons.
Don’t forget one semi-feasible idea : aneutronic fusion and direct energy conversion.
In short, you get a small amount of boron and hydrogen to reach temperatures of a billion degrees and incredible pressures. (in theory achievable through various trickery with big honking magnetic or electric fields or lasers)
They fuse. You get as a primary product positively charged helium ions that are several percent of the speed of light.
There is some way to decelerate them using wire meshes with big electric fields, and the deceleration induces current you can use in a circuit. I don’t have the slightest idea how, other than to say this sounds like a cathode ray tube running in reverse.
It’s “semi-feasible” in that if it worked, it would give you an amazingly lightweight* power source that is better than basically anything else we can make. It would also give you one of the best performing rocket engines ever thought of. (better than antimatter for travel within our solar system because while the ISP is much lower, the thrust is a lot higher)
The helicarrier could actually fly, and stay aloft*, if it were powered by a hydrogen-boron fusion reactor. You’d actually get so much power you could keep superconducting motors turning rotors fast enough for enough lift to stay airborne. And you would only be consuming a tiny trickle of boron, enough to fly for years on onboard fuel. (you’d get the hydrogen from water vapor in the air. Also note that the rotor blades would need to be a lot bigger than the ones shown in the movies, and you’d use a lot more than 4 lift rotors)
The “semi” part is that apparently it is insanely difficult to contain the plasma at the needed temperatures and pressures, it takes the most complex and expensive equipment our civilization can make, and there is skepticism and lack of empirical data proving that any design will work.
*as a weapon the helicarrier is awful. It’s a slow moving, immensely expensive target and enemy nations would develop nuclear-tipped air to air missiles to deal with it easily.
*the reason it would be light is that a large fusor would not have that much mass relative to it’s power output, as most of it would be superconducting magnets. And the conversion apparatus would be very light. And you wouldn’t, in theory, need radiation shielding though in practice you likely would.
Curious about that, too. If I could power stuff with my metabolism I’d be plugged in all day and losing weight while I sit on my bottom at work! Count me in.
Hmmmm … β-Franklin?