An assembled battery unit, comprising: an assembled battery having a plurality of cells (11 -11(x)) electrically connected in series; a voltage detection unit configured to measure a voltage of each of the cells; a current detection circuit connected parallel to a current detection resistor connected in series to a negative electrode of the assembled battery; discharge resistors (31r -31r(x+1)) each connected to an electrode of each of the cells; discharge switches (SW -SW(x-1)) which are respectively connected to every pair of the discharge resistors each corresponding to each of the cells, and provided to electrically open and close the connection; a charge amount difference detection circuit configured to calculate charge amount differences greater than a charge amount of a reference cell, which is the cell from the plurality of cells that reaches a predetermined specific voltage last, from values of voltage and current received from the voltage detection unit and the current detection circuit, wherein the charge amount differences of the cells are calculated by integrations of the charging or discharge currents during a period corresponding to the time differences between the reference cell and the other cells reaching the predetermined specific voltage; a discharge time conversion unit configured to receive the charge amount differences for each cell from the charge amount difference detection circuit and to calculate the length of time to close each discharge switch; and a switch controller configured to receive the length of time to close each discharge switch and to control the opening and closing of the discharge switches. an assembled battery having a plurality of cells (11 -11(x)) electrically connected in series; a voltage detection unit configured to measure a voltage of each of the cells; a current detection circuit connected parallel to a current detection resistor connected in series to a negative electrode of the assembled battery; discharge resistors (31r -31r(x+1)) each connected to an electrode of each of the cells; discharge switches (SW -SW(x-1)) which are respectively connected to every pair of the discharge resistors each corresponding to each of the cells, and provided to electrically open and close the connection; a charge amount difference detection circuit configured to calculate charge amount differences greater than a charge amount of a reference cell, which is the cell from the plurality of cells that reaches a predetermined specific voltage last, from values of voltage and current received from the voltage detection unit and the current detection circuit, wherein the charge amount differences of the cells are calculated by integrations of the charging or discharge currents during a period corresponding to the time differences between the reference cell and the other cells reaching the predetermined specific voltage; a discharge time conversion unit configured to receive the charge amount differences for each cell from the charge amount difference detection circuit and to calculate the length of time to close each discharge switch; and a switch controller configured to receive the length of time to close each discharge switch and to control the opening and closing of the discharge switches.