Cochlear implants (CIs) are used for compensating the so-called deep sensorineural deafness. CIs are usually powered by rechargeable or long-lasting batteries. In this paper, the feasibility of a fully implanted stand-alone device able to provide the electric power required for stimulating the auditory nerve, without external recharging, is investigated. At first, we demonstrate that the sound wave entering the ear is not a sufficient power source. Then, we propose a solution exploiting the mechanical energy associated to head vibration during walking. The energetic feasibility of this approach is demonstrated based on experimental measurements of head motions. Preliminary considerations on the technical feasibility of a fully implanted energy harvester are finally presented.