A battery charging method that detects the voltage of each series-connected battery, discharges batteries with voltage exceeding a prescribed voltage, and charges a plurality of batteries while maintaining cell balance. This charging method detects the voltage of each battery being charged and if any battery voltage exceeds the prescribed voltage, only the battery that exceeds the prescribed voltage is discharged, after a specified charging time, until its voltage drops to the prescribed voltage. Batteries that do not exceed the prescribed voltage are not discharged, and thereby all batteries are charged while balancing their voltages.