Battery charger, secondary battery unit and electric apparatus equipped therewith

A mobile telephone has a rechargeable battery, and the rechargeable battery is charged through a battery charger; the battery charger includes an information processing system serving as a charge controller and a battery manager; the battery manager measures a discharging time period of the rechargeable battery so as to store pieces of duration data expressing a charge-and-discharge cycle, and determines a charge initiation level and a charge completion level on the basis of the pieces of duration data in such a manner to reduce the number of charging operation without shortage of electric charge for the rechargeable battery; and the charge controller carries out the charging with reference to the charge initiation level and charge completion level so that the rechargeable battery is prolonged in life time.