In general, in the circuit to measure and diagnose the cell post voltage and internal impedance in storage battery cells and find out their aging status, the impedance voltage signal which is induced by the constant current is added to the direct current voltage on the storage battery cell post. This invention provides a much better method to discriminate the battery cell voltage 1.0 V-12 V and internal impedance voltage from the various noises on the battery cell post voltage like the induced ripple voltage, and then convert them to digital values by means of a A/D converter, and input the digital signals into a CPU. As a result, it raises the degree of accuracy in measurement of the internal impedance value of the battery.