Detection on SOC of VRLA battery with EIS

In this paper, one of the nondestructive detection techniques, electrochemical impedance spectroscopy (EIS), is adopted to detect the state of charge (SOC) of valve regulated lead acid (VRLA) battery under different conditions. Those conditions include off-line (open circuit) and on-line (discharging). Battery which is discharged with 0.1C is measured off-line in different SOC. As for the on-line group, batteries are discharged with different proportions of rated capacity which are 0.1 C, 0.5C and 1C, sequentially. The measurement results and the built equivalent electrical model can verify each other with curve fitting analysis and information hidden in the measurement results can be discovered with curve fitting analysis. Value and error % of all electrochemical elements can be compared after analysis so that observation on the relations between electrochemical elements and SOC can be implemented. Parameters belong to impedance category are inversely proportional to SOC; however, parameters belong to capacitance category are approximately proportional to SOC. In addition to variations of every electrochemical element, how position of battery change under different circumstances can be observed easily. The feasibility of detection on the SOC of battery with EIS can be ensured after series experiments and analysis.