Use of AC impedance/conductance and DC resistance for determining the reliability of VRLA battery systems

The reliability of valve-regulated lead-acid (VRLA) cells has been an issue in the light of the relative immaturity of this technology. AC impedance/conductance is being promoted as a means of determining their ´state of health´, as signified by their ability to perform electrically to end of life. Claims have been made that the higher the conductance, or the lower the impedance, the better the battery. The authors´ efforts have focussed on evaluating this and similar techniques towards the goal of determining VRLA battery performance and reliability. Impedance and conductance measurements were made on large number of VRLA cells and batteries in the size range of 25 to over 2000 Ah, using several different commercially available meters. Data on new as well as naturally and artificially aged cells and batteries are discussed as are extended performance data and teardown analysis of cells at end of life. Results from DC resistance, measured by a voltage-relaxation technique, are also compared and correlated with that from impedance/conductance.