Certain embodiments provide battery system including: a battery; a current measurement unit configured to measure a current charged to or discharged from the battery; a voltage measurement unit configured to measure an output voltage of the battery; a function creation unit configured to create a function representing a depth-of-discharge characteristic of the battery on the basis of the measured current and output voltage; and a remaining capacity calculation unit configured to calculate a remaining capacity corresponding to the output voltage of the battery using the created function.