Evaluation of the relationship between conductance and capacity measurements of VRLA batteries in Brazil

Since 1996 CPqD has been studying the application of conductance and impedance techniques to evaluate the degree of degradation of stationary lead acid batteries. The conductance technique has becoming a popular technique in Brazilian´s telecommunications companies since 2002, and a very frequent question is: - which is the relationship among measurements of conductance and capacity? In order to clarify this question we decided to make some experiments. In these experiments the charge/discharge cycles was accelerated, each one composed by 23 hours of charge and a discharge at C₁, (until that the voltage of the last cell has reached 1,75 V). This experiment was done with three VRLA AGM (absorbed glass material) cells. In each cycle the conductance of each cell was measured before beginning the discharge, and the experiment was conducted until two cells reached a capacity below 50% of the nominal value. This paper reports the results obtained in accelerated life cycle testing, the relationship between conductance and capacity, the number of cycles supported by each cells, and a determination whether it is possible or not to estimate the capacity through conductance measurements.