Patent ID: 7298113

Claim:
A battery pack having a secondary battery, comprising: a holding unit for detachably holding a primary battery; a switch for switching a voltage of said primary battery and a voltage at an external terminal; a voltage converter to which either said primary battery voltage or said external terminal voltage selected by said switch is inputted and which supplies a stabilized output voltage to a positive polarity side of said secondary battery; a protecting unit that performs overcharge, overdischarge and overcurrent protection; a control unit for controlling said switch so as to select said external terminal voltage in a normal state and, when said primary battery is attached, select said primary battery voltage; and a light emitting device that is turned on only in the state where said secondary battery is charged by either said primary battery voltage or by said external terminal voltage, wherein, said control unit is a switch which is provided for said holding unit and detects that said primary battery has been attached, and a light emitting device light-on switch is turned on when an output terminal of an AND gate is equal to “1” and a detection signal of said detecting switch is inputted to one input terminal of the AND gate and a charge control signal from said protecting circuit is supplied to the other input terminal of the AND gate.