This is where I started, as I have more of a biochem bg… but it seems exceptionally difficult even conceptually, without trying to pack all of the necessary reactions into a tiny capsule.
Induction or something like what @NatTheCat is proposing feel like a great solution for things that we can’t wait to develop specialized technology for, but it seems like a good “moonshot” to aim for a fully contained system… again, perhaps it is a pipe dream 
Amazing! Exactly what I had in mind, thanks for bringing that to the surface. Amal does bring up an important point in that thread though:
Perhaps the piezoelectric supply would result in a more accessible end technology?
Yeah I am still unsure about batteries, at least in myself… If someone needs a pacemaker I think the risk of a deep-tissue battery is probably less relevant to the decision. But perhaps they are still viable for consumer implants, they could simply have a shorter lifespan or something.