Second‐Order Harmonic in the Current Response to Sinusoidal Perturbation Voltage for Lead‐Acid Battery An Application to a State‐of‐Charge Indicator

Distortion of the current response to sinusoidal alternating perturbation voltage has been quantitatively measured as a function of state of charge for commercially available lead-acid batteries. The input amplitude adopted here was greater than those used for ordinary impedance measurement. The distortion is represented as a power spectrum. Among higher order harmonics, that of the second one was selected for the parameter of a state-of-charge indicator. Excellent linearity was observed for the state of charge. It was also clarified that, compared to other parameters of the indicator, such as terminal voltage, impedance of fundamental tone, and concentration of sulfuric acid this parameter is less influenced by other factors during practical operation, such as discharge current and rest time.