an electrical power management system for supplying power to a computer peripheral having a relatively high intermittent power demand , such as a packet - switched data radio . a first self - contained rechargeable power supply , outputting power appropriate for the electrical appliance , stores electrical energy and supplies power to the appliance . a second self - contained rechargeable power supply stores electrical energy and supplies electrical power to intermittently recharge the first power supply . the first and the second power supplies can be such self - contained units as single or multicell batteries or capacitors . preferably , the first power supply is a battery or a capacitor and the second power source is an internal power supply of a portable personal computer .