[yazaddaruvala]

My understanding is this isn't possible because of the size/invasiveness.

We need significantly better power sources that are either have lots of energy capacity, xor some energy capacity and able to charge while inside the body.

Either version they need to be small enough that the procedure is cheap and the body doesn't reject the device. Additionally, anything like this would need to go through regulatory bodies for medical devices, and would not be approved for "healthy people" (i.e. significantly reduced adoption).

Roughly putting us back to non-invasive.