Performance measurement and reliability of VRLA batteries. II. The second generation

This paper presents the results of capacity discharge tests on approximately 15000 VRLA cells, of primarily AGM design, representing five different US manufacturers' "20 year design life" products. Some data are also presented on gel design cells. Just as was found by D.O Feder (see INTELEC 95, The Hague, Netherlands, IEEE, p.22-8, 1995) the cells showed significant premature capacity loss beyond 2 years of service in benign, temperature controlled environments. The cells tested generally represented designs that were too new to have been included in the earlier study. While it had been hoped that these newer design cells would have been modified to correct the early failures shown in those tested in 1995, this was apparently not to be. In accord with that study, as well as an extensive Swedish study of 35000 VRLA batteries, presented at INTELEC 95, the most significant conclusion from all these studies is that VRLA cells, regardless of manufacturer or design, demonstrate acceptable reliability for only 2 years.