Cell deterioration diagnostic based on integrated value

A cell deterioration diagnostic device configured to diagnose cell deterioration of a rechargeable secondary cell having a cell internal voltage, a cell internal impedance, and a cell inter-terminal voltage, the device comprising:

• a charging circuit configured to supply a charging electrical current to the secondary cell to charge the secondary cell, and to cause the cell inter-terminal voltage to increase above the cell internal voltage over time in accordance with a charging transient characteristic;
• the charging circuit being interrupted in operation to discharge the secondary cell and cause the cell inter-terminal voltage to decrease towards the cell internal voltage over time in accordance with a rest time transient characteristic;
• a voltage detector connected across the secondary cell and configured to measure the cell inter-terminal voltage at predetermined sampling frequencies over the rest time transient characteristic;
• a storage unit configured to store potential differences between the cell inter-terminal voltage and the cell internal voltage at the sampling frequencies over the rest time transient characteristic;
• a calculating unit configured to integrate the stored potential differences to obtain an integration value;
• and
• a diagnosis unit configured to diagnose the cell deterioration of the secondary cell based on the integrated value.