A battery management system for a cell group including a plurality of battery cells (B_1,..., B_N) connected in parallel, the battery management system comprising: a displacement sensor configured to detect a displacement of the cell group in a stack direction of the plurality of battery cells; and a control unit operably coupled to the displacement sensor, wherein the control unit is configured to: detect the displacement of the cell group at a predetermined time interval for a first diagnosis period from a first time point to a second time point during charging of the cell group, wherein the first time point is a time point at which a state of charge of the cell group reaches a first reference value, and the second time point is a time point at which the state of charge reaches a second reference value, determine a first displacement curve from a history of the displacement of the cell group over the first diagnosis period, wherein the first displacement curve indicates a relationship between the displacement of the cell group and the state of charge for the first diagnosis period, characterized in that the control unit is further configured to: determine whether the plurality of battery cells is nonuniformly degraded based on the first displacement curve by: determining a first differential displacement curve from the first displacement curve, wherein the first differential displacement curve indicates a relationship between a differential value of the displacement of the cell group and the state of charge for the first diagnosis period, and determining that the plurality of battery cells is nonuniformly degraded in response to a total number of peaks of the first differential displacement curve being equal to or larger than a threshold number, or in response to a distance between a first peak and a last peak of the first differential displacement curve being equal to or larger than a threshold distance. a displacement sensor configured to detect a displacement of the cell group in a stack direction of the plurality of battery cells; and a control unit operably coupled to the displacement sensor, wherein the control unit is configured to: detect the displacement of the cell group at a predetermined time interval for a first diagnosis period from a first time point to a second time point during charging of the cell group, wherein the first time point is a time point at which a state of charge of the cell group reaches a first reference value, and the second time point is a time point at which the state of charge reaches a second reference value, determine a first displacement curve from a history of the displacement of the cell group over the first diagnosis period, wherein the first displacement curve indicates a relationship between the displacement of the cell group and the state of charge for the first diagnosis period, characterized in that the control unit is further configured to: determine whether the plurality of battery cells is nonuniformly degraded based on the first displacement curve by: determining a first differential displacement curve from the first displacement curve, wherein the first differential displacement curve indicates a relationship between a differential value of the displacement of the cell group and the state of charge for the first diagnosis period, and determining that the plurality of battery cells is nonuniformly degraded in response to a total number of peaks of the first differential displacement curve being equal to or larger than a threshold number, or in response to a distance between a first peak and a last peak of the first differential displacement curve being equal to or larger than a threshold distance. detect the displacement of the cell group at a predetermined time interval for a first diagnosis period from a first time point to a second time point during charging of the cell group, wherein the first time point is a time point at which a state of charge of the cell group reaches a first reference value, and the second time point is a time point at which the state of charge reaches a second reference value, determine a first displacement curve from a history of the displacement of the cell group over the first diagnosis period, wherein the first displacement curve indicates a relationship between the displacement of the cell group and the state of charge for the first diagnosis period, characterized in that the control unit is further configured to: determine whether the plurality of battery cells is nonuniformly degraded based on the first displacement curve by: determining a first differential displacement curve from the first displacement curve, wherein the first differential displacement curve indicates a relationship between a differential value of the displacement of the cell group and the state of charge for the first diagnosis period, and determining that the plurality of battery cells is nonuniformly degraded in response to a total number of peaks of the first differential displacement curve being equal to or larger than a threshold number, or in response to a distance between a first peak and a last peak of the first differential displacement curve being equal to or larger than a threshold distance.