A battery system comprising: a battery module including a plurality of battery sub modules connected in parallel between system terminals; a plurality of switches connected in series to the plurality of battery sub modules, respectively; a measuring unit arranged to measure voltage values of the battery module and/or cells included in the battery module and current values which flow on the battery modules; a detecting unit arranged to determine whether or not an internal short occurs in the plurality of battery sub modules by monitoring the voltage values or the current values; and a control unit arranged to control, when the internal short occurs in at least one battery sub module of the plurality of battery sub modules, at least one switch corresponding to the at least one battery sub module in a non-conductive state among the plurality of switches, characterized in that the detecting unit is arranged to determine each of a first voltage average in a first time period and a second voltage average in a second time period for each cell included in the plurality of battery sub modules based on the voltage values measured by the measuring unit and to determine that the internal short occurs with respect to a cell in which a value acquired by subtracting the second voltage average from the first voltage average is equal to or larger than a first threshold, when the battery module is in constant current charging, and the second time period includes a time period after the first time period; or the detecting unit is arranged to determine each of a first current average in a first time period and a second current average in a second time period for each battery sub module based on the current values measured by the measuring unit and to determine that the internal short occurs with respect to a battery sub module in which a value acquired by subtracting the first current average from the second current average is equal to or larger than a third threshold, when the battery module is in constant voltage charging, and the second time period includes a time period after the first time period; or the detecting unit is arranged to determine each of a first voltage average in a first time period and a second voltage average in a second time period for the cells included in the plurality of battery sub modules based on the voltage values measured by the measuring unit and to determine that the internal short occurs with respect to a cell in which a value acquired by subtracting the second voltage average from the first voltage average is equal to or larger than a sixth threshold among the cells, after a predetermined time elapsed from a charging termination time point of the battery module, and the second time period includes a time period after the first time period. a battery module including a plurality of battery sub modules connected in parallel between system terminals; a plurality of switches connected in series to the plurality of battery sub modules, respectively; a measuring unit arranged to measure voltage values of the battery module and/or cells included in the battery module and current values which flow on the battery modules; a detecting unit arranged to determine whether or not an internal short occurs in the plurality of battery sub modules by monitoring the voltage values or the current values; and a control unit arranged to control, when the internal short occurs in at least one battery sub module of the plurality of battery sub modules, at least one switch corresponding to the at least one battery sub module in a non-conductive state among the plurality of switches, characterized in that the detecting unit is arranged to determine each of a first voltage average in a first time period and a second voltage average in a second time period for each cell included in the plurality of battery sub modules based on the voltage values measured by the measuring unit and to determine that the internal short occurs with respect to a cell in which a value acquired by subtracting the second voltage average from the first voltage average is equal to or larger than a first threshold, when the battery module is in constant current charging, and the second time period includes a time period after the first time period; or the detecting unit is arranged to determine each of a first current average in a first time period and a second current average in a second time period for each battery sub module based on the current values measured by the measuring unit and to determine that the internal short occurs with respect to a battery sub module in which a value acquired by subtracting the first current average from the second current average is equal to or larger than a third threshold, when the battery module is in constant voltage charging, and the second time period includes a time period after the first time period; or the detecting unit is arranged to determine each of a first voltage average in a first time period and a second voltage average in a second time period for the cells included in the plurality of battery sub modules based on the voltage values measured by the measuring unit and to determine that the internal short occurs with respect to a cell in which a value acquired by subtracting the second voltage average from the first voltage average is equal to or larger than a sixth threshold among the cells, after a predetermined time elapsed from a charging termination time point of the battery module, and the second time period includes a time period after the first time period.