A rechargeable power supply including voltage protection means through voltage dependent disconnecting means. A rechargeable power supply comprises at least one rechargeable cell connectable to a power source, a Zener diode connected to the at least one cell, and a bipolar transistor or a FET for selectively disconnecting the Zener diode from the cell in order to reduce any discharge of the cell through the voltage protection means. The Zener diode and the transistor are connected together in series and jointly connected across the cell in parallel.