Abstract: A hybrid battery pack and a power supply procedure for supplying power to a mobile computing system comprising a Li polymer battery coupled in parallel with a supercapacitor cell battery. The Li polymer battery supplies substantially all the continuous currents demanded by the system load. The supercapacitor cell battery supplies substantially all the transient current demanded by the system load. A charging control logic circuit is coupled to the power source and the system load, and operable to control the Li polymer battery to charge the supercapacitor cell battery at a constant rate while the supercapacitor cell battery supplies current to the system load. The control logic can also send instructions to have system load reduced if the supercapacitor cell battery is depleted before it can be charged with an external charger.