CHARGER AND METHOD FOR DETECTING COMPLETION OF CHARGING

PURPOSE:To prevent shortening of the service life of a battery by measuring the inner resistance of the battery at a predetermine period and ending the charging operation at a moment when an inner resistance for ending the charging operation is detected. CONSTITUTION:A charge control circuit section 7 measures the open voltage of a battery 2 through an A/D converter 4 and turns the contact of a common terminal in a relay switch 5 to the terminal (d) side thus measuring the load connection voltage, i.e., the voltage when a load 6 is connected with the battery 2, through a relay switch 3 and the A/D converter 4. The charge control circuit section 7 then calculates the inner resistance of the battery 2 based on the open voltage and the load connection voltage thus measured. When the calculated inner resistance represents a charge end resistance, the residual charging amount is presented on a display section 8 and then the charging is ended and switched to trickle charging. This method prevents overcharge and thereby prevents shortening of the service life of battery 2.