The use of impedance measurement as an effective method of validating the integrity of VRLA battery production

The response of batteries to an injection of AC current to give an indication of battery state-of-health has been well established and extensively reported over a number years but it has been used largely as a means of assessing the condition of batteries in service. In this paper the use of impedance measurement as a quality assurance procedure during manufacture will be described. There are a number of commercially available meters that are used for monitoring in field operations but they have not been developed for use in a manufacturing environment. After extensive laboratory testing a method specifically designed for impedance measurement system at the end of manufacturing lines in order to assure higher product integrity was devised and validated. A special testing station was designed for this purpose and includes battery conditioning prior to the test and sophisticated software driven data analysis in order to increase the effectiveness and reliability of the measurement. The paper reports the analysis of the data collected over two years of monitoring of the entire production with the impedance testing station at the end of the production line. Data comparison with earlier production shows an increase in the number of batteries scrapped internally and correspondingly a reduction in the number of defective products reaching distribution centres and also the field. The accumulated experience has also been very helpful in getting better information about the effect of the various parameters that affect the measured impedance value and this will assist in improving the reliability of impedance measurements in field service.