A charging accessory for a portable electronic device has an input/output port for providing electrical connections to an input/output port of the device. The accessory includes a charger for charging the battery of the portable electronic device and a discharging circuit for discharging the battery of the device. A processor in the accessory determines when the device battery is fully charged and fully discharged. A time stamp associated with a charging/discharging cycle and device identification information identifying the particular device upon which the charging cycle was performed is stored in a memory of the accessory. The charging accessory then automatically performs a discharging/charging operation for the device according to a predetermined schedule to recalibrate a battery level display of the device whenever the accessory is coupled to the device.