An implantable medical device includes an energy storage device with an internal component and an outer case that encloses the internal component. The outer case is electrically connected to the internal component. The energy storage device includes a first electrode that is electrically connected to the internal component. Furthermore, the device includes a control assembly with a control component and a control case that encloses the control component. The control case is coupled to and electrically connected to the outer case. The control component is electrically coupled to the first electrode and the outer case to be powered by the internal component of the energy storage device. The control component controls transmission of an electrical signal between the implantable medical device and biological tissue. Also, an outer surface of the outer case and the outer surface of the control case are exposed to the biological material.