An electronic device includes a battery module, a power supply, a power controller, and a processor. The power controller obtains an initial battery capacity of the battery module and a current time when the power supply is connected to an external power supply. The processor sets a preset target battery capacity and a charging completion time, obtains a charging battery capacity according to the preset target battery capacity, the initial battery capacity and a charging time interval, calculates a calculated battery capacity-time-ratio according to the charging battery capacity and the charging time interval, converts the calculated battery capacity-time-ratio into a charging battery capacity, and transmits it to the power controller. The power controller converts the supplied power to a charging voltage or a charging current correspondingly according to the charging battery capacity, to charge the battery module to the preset target battery capacity by a charging end time.