The implantable portion of a cochlear implant system [cochlear implant (CI)] that typically consists of an electrically-powered electrode array surgically implanted in one cochlea, and a receiver-stimulator implanted in the skull near the ear and connected to the electrode array; it does not elute a drug. Electrical signals are transmitted from the external portion of the device to the receiver-stimulator and ultimately to the cochlea, via the electrode array, for the partial restoration of auditory sensation in a severely/profoundly deaf person. Dedicated implantation instruments may be included.