A power supply system to operate an implanted electric-powered device such as a blood pump. A secondary coil having a biocompatible covering is implanted to subcutaneously encircle either the abdomen or the thigh at a location close to the exterior skin. The secondary coil is electrically interconnected with an implanted storage battery and the blood pump. A primary coil of overlapping width is worn by the patient at a location radially outward of the secondary coil. An external battery plus an inverter circuit in a pack is attached to a belt having a detachable buckle connector which is conventionally worn about the waist. Efficient magnetic coupling is achieved through the use of two air-core windings of relatively large diameter.