I apologize if this is a silly question. The reason I ask is I'm wondering if it would be possible to build a fuel cell that runs on body fat. I know ones for butane exist, could they work for this? If not, is there any good reason it isn't possible?
Basically I'm imagining some kind of flexible inductive charger in your hand, or wrist for a smart watch, and connected to a fuel cell that's connected to the circulatory system and runs off body fat.
It just seems silly to lug external batteries along on long on bike rides when the whole point of the ride is to get rid of excess chemical energy anyway.
I obviously don't have the skills to pursue this, but I just want to know if the dream is silly. :)