In a battery monitoring system included in a secondary battery, high-accuracy charge control is enabled at low cost. A semiconductor device includes: a drive unit which drives a transistor for controlling the charge current of a secondary battery and which is configured to be capable of selecting one of plural different voltages as a drive voltage (VGC) for turning on the transistor; and a data processing control unit which performs program processing. The data processing control unit generates condition information including information about the battery level of the secondary battery based on measured values of the secondary battery voltage and current and adjusts the charge current of the secondary battery by changing the drive voltage selection.