EVALUATING THE STATE-OF-HEALTH OF FLOODED AND VALVE-REGULATED LEAD-ACID-BATTERIES - A COMPARISON OF CONDUCTANCE TESTING WITH TRADITIONAL METHODS

In a previous series of studies, field and laboratory examinations wer e made of the relationship of both traditional cell-testing parameters and conductance testing with actual capacity testing for approximatel y 500 valve-regulated lead/acid (VRLA) cells of various sizes and desi gns, and in various applications. It was concluded that a significant number of VRLA cells had suffered premature capacity loss, that was no t detected satisfactorily by the individual cell float-voltage or by s pecific-gravity (calculated) measurements. In contrast, the data showe d a high degree of correlation between cell capacity and cell conducta nce. This study provides additional evidence of the extent of prematur e capacity degradation of VRLA cells, and includes cells of newer desi gns. It quantifies, more explicitly, the inability of cell float-volta ges or specific gravity to provide early warning of these significant failures in capacity. It provides additional data that demonstrate the high degree of correlation between conductance and capacity, and pres ents striking evidence of the ability of conductance testing to provid e early warning of premature capacity failure of VRLA cells. Additiona l data are given on teardown postmortum analyses of a series of cells that exhibit a wide range of measured capacities. Although the establi shed failure modes among these cells are significantly varied, it is e xtremely encouraging to report that cell performance is accurately pre dicted by the conductance values obtained. A report is also given of t he results of initial tests of conductance/capacity relationships in f looded lead/acid cells, i.e., of the type used by both electric power utilities and telecommunications organizations to provide stand-by res erve power. The accuracy of conductance data to predict, correctly, ce ll capacity behaviour is contrasted with predictions that result from the conventional test parameters of cell float-voltages and measured s pecific gravities. Again, with flooded cells, the data indicate a sign ificantly improved capability to detect low-capacity cells, based on c onductance, than would be obtained from either cell float-voltage or s pecific-gravity measurements.