Ear powered batteries use the body itself as a fuel cell - promising an "unlimited lifespan" (assuming the host is immortal I guess).
Researchers have for the first time harvested the energy of the inner ear to power a small sensing device. The electric potential of the cochlea
operates like a biological battery and is critical for transforming sound pressure waves into the electrical signals sent to the brain. Now,
scientists have developed a chip that can harness this electrical energy without interfering with normal hearing...
...Many other devices designed to extract power from living organisms use enzymes to convert catalytic energy into electrical energy, but the new chip
“just steals a little bit of energy the body produces itself.”
...The strategy could address one of the drawbacks of using biofuel cells—namely that the enzymes used to harvest energy from blood glucose have a
limited lifespan, ...But in the inner ear, the body is itself a fuel cell with unlimited lifespan.