Battery charger

A battery charger detects a battery voltage, a battery temperature, and computes a change in the battery voltage between two timings at which the battery voltages are detected and also a change in the battery temperature between two timings at which the battery temperatures are detected. A charge current is determined based on the battery voltage gradient information, the battery temperature gradient information, and at least one of the battery voltage information and the battery temperature information. Also, a full charge discrimination value is also determined based on at least three parameters mentioned above. The battery is determined to be a full charge condition when the computed battery temperature change has exceeded a sum of the minimum battery temperature gradient value and the full charge discrimination value.