Secondary battery device

According to one embodiment, a device includes an assembled battery (10) including cells (BT), a circuit (20) which measures a potential difference of each cell (BT), a current detector (30) which detects a value of a current in the assembled battery (10), a determination module (52) including a first reference (L1) and a second reference (H1) which determines whether the potential difference is higher than the first reference (L1) and is lower than the second reference (H1), and a module (54) which calculates a charge/discharge capacity, based on a current integration value which is detected by the current detector (30), when the determination module(52) determines that the potential difference is higher than the first reference (L1) and is lower than the second reference (H1), and calculates the charge/discharge capacity, based on a state of charge corresponding to the potential difference, when the determination module (52) determines that the potential difference is not higher than the first reference (L1) or is not lower than the second reference (H1).