METHOD AND DETECTION UNIT FOR DETECTING INHOMOGENEOUS CELL PERFORMANCE OF A BATTERY SYSTEM

The present invention refers to a method and a detection unit (1) for detecting inhomogeneous cell performance of a battery system comprising a plurality of battery cells, comprising: determining a charging resistance ratio (ResRtoChg), which is the ratio of a maximum cell charging resistance (ResChgMax) of a battery cell among a plurality of battery cells and an average cell charging resistance (ResChgAvg) of the plurality of battery cells, each determined in response to a charging current (I) applied to the battery cells; and/or determining a discharging resistance ratio (ResRtoDch), which is the ratio of a maximum cell discharging resistance (ResDchMax) of a battery cell among a plurality of battery cells and the average cell discharging resistance (ResDchAvg) of the battery cells, each determined in response to a discharging current (I) applied to the battery cells; and determining that the battery system is in a degraded ageing state, when at least one of the determined charging resistance ratio (ResRtoChg) and/or the determined discharging resistance ratio (ResRtoDch) is above a predetermined threshold value; and determining that the battery system is in a non-degraded ageing state, when none of the determined charging resistance ratio (ResRtoChg) and/or the determined discharging resistance ratio (ResRtoDch) is above the predetermined threshold value.