An implantable energy storage system for a medical implant, which is provided with a rechargeable storage for electric energy and a unit for controlling the charging process. The system includes a monitoring unit which is independent of the control unit and which senses the storage voltage independently of the control unit and is designed such that it assumes control of the charging path when the sensed storage voltage lies outside a predetermined range. Furthermore, a corresponding process for operating the implantable energy storage system is provided.
