Lead acid battery has been one of the most important secondary battery for industrial use. It has been revealed that the corrosion of current collector (CC) is a critical factor to determine the battery life.(1-4) In this study, focusing on the local cell reaction (LCR) between the cathode active material and CC during the rest time period, we investigate the capacity fading mechanism of the lead acid battery. Only when the lower potential material in comparison with the cathode active material is employed as CC, formation of alpha-PbO2 is detected accompanied by the capacity degradation. We clarified that LCR of CC results in the alpha-PbO2 formation, which correlates with the degradation of the cell performance. (C) 2016 The Electrochemical Society. All rights reserved.