Implants that don't need an external charge could make it easy to aid hearing.

from arstechnica.com

key words: cochlea chip,  self-sufficient, self-powering implants

Inner ear implant uses biological battery to self-charge. A team of surgeons, neuroscientists, and electrical engineers has developed a cochlea chip that extracts electrical signals from the inner ear to power itself. The chip is the latest in a series of inventions aimed at creating entirely self-sufficient, self-powering implants that will remove the need for external power and enable permanent surgical implantation in some cases. This year alone, Stanford University announced the creation of its radio wave-powered heart implant and infrared light-powered retinal implants.

Cochlear implants have been around for decades, with the first electrical stimulation of auditory nerves taking place in the 50s. Though the implant has been a great success, with hundreds of thousands of people with severe hearing difficulties receiving the implant each year, they still run on batteries so are fairly cumbersome. MIT hopes to change all that by taking advantage of a natural battery that lies dormant within the ear.

"In the past, people have thought that the space where the high potential [in the ear] is located is inaccessible for implantable devices, because potentially it's very dangerous if you encroach on it," said Konstantina Stankovic, an otologic surgeon at the Massachusetts Eye and Ear Infirmary. "We have known for 60 years that this battery exists and that it's really important for normal hearing, but nobody has attempted to use this battery to power useful electronics."

Full text at: 

http://arstechnica.com/science/2012/11/inner-ear-implant-uses-biological-battery-to-self-charge/