A hybrid power supply includes a switching type DC/DC boost type converter that receives energy from a primary battery cell and is arranged to deliver the energy to a rechargeable cell, set to provide a fixed output voltage that is less than the full charge voltage of the rechargeable cell. The hybrid power supply includes a circuit including a primary battery current control that senses primary battery current, and controls in part operation of the converter to provide constant current discharge on the primary battery side of the hybrid power supply.