Abstract: Based on the measurement of the increase of sinusoidal voltage ?V=Vmaxsine(2?ft) on adding a sinusoidal current ?I=Imaxsine(2?ft+?) to the battery current, where f is the frequency and Imax, the amplitude of the superimposed current, with whose magnitudes the electrochemical impedance of the battery Z(f)=Vmax/Imaxej? is calculated, comprising the application of a first sinusoidal signal of prefixed frequency to the battery which generates an alternate voltage component superimposed over the direct one; eliminating the direct component of the response signal; applying a second periodic voltage signal with a frequency identical to that of said first signal and carrying out a synchronous detection of the alternate component generated by the application of said first signal to obtain the voltage proportional to the electrochemical impedance and evaluate the state of health and charge of the battery.