Patent ID: 7696723

Claim:
A battery charger comprising: a charging device for charging a secondary battery; a voltage detector for detecting a voltage value of the secondary battery; a temperature sensor for sensing an environmental temperature; a controller for sensing an environmental temperature by said sensor and the voltage values of the secondary battery by said voltage detector of the secondary battery before charging to judge a charging condition, the charging condition based on whether a detected voltage value falls within a predetermined range of threshold values, and for receiving voltage values of the secondary battery as detected by said voltage detector at a predetermined time interval while the secondary battery is being charged by said charging device, and for judging a charging condition of the secondary battery based on a rate of change of the received voltage values; and a display for displaying information, wherein said controller controls to display a condition sign that indicates the judged charging condition of the secondary battery on said display, wherein the displayed judged charging condition is classified stepwise to a plurality of successive charging conditions, wherein a first one of the successive charging conditions corresponds to a first predetermined range of threshold values, a second one of the successive charging conditions corresponds to a second predetermined range of threshold values that is higher than the first predetermined range, and a third one of the successive charging conditions IS associated with a third predetermined range of threshold values that is higher than the second predetermined range, and wherein each of the predetermined ranges of threshold values are functions of and are inversely related to the environmental temperature sensed by the sensor; and, wherein said controller performs discharging in a short time before detecting the voltage value of the secondary battery.