Investigation of the Influence of Active Material Structure on High Rate Discharge Performance of VRLA Batteries

The following paper presents a simple but effective technique to monitor ageing, deterioration and failure modes of valve regulated lead acid (VRLA) batteries. The investigation primarily deals with high rate discharge products subjected to long standing times in hot environmental conditions, although could be adjusted to products and operating conditions. The technique presented in this paper, was tested and verified by using results obtained from experiments conducted at the YUASA battery laboratories and the CAPSE labs at the University of South Wales (USW). The results indicate that the positive active material was the major cause for low discharge performance with the electrochemical analysis of the battery showing the presence of significant levels of unconverted lead sulphate (5.52 %). Further detailed investigations within this paper also show other key factors that could limit the surface available for the electrolyte to diffuse into the plates, and consequently limit the overall efficiency of the battery. These aspects include the build-up of large lead sulphate crystals, which are difficult to break down in the charge process and may have arisen during the standing time period at high temperature, where the batteries experience accelerated self-discharge.