Life prediction for valve regulated lead acid batteries from early current/voltage data

Abstract

Summary form only given. As valve regulated lead-acid (VRLA) batteries age, they demonstrate a predictable drop in end-of-charge voltage and concomitant rise in end-of-charge temperature. This is attributed to the increasing dominance of the oxygen recombination cycle, which results from the negative plate not being fully charged over several cycles. Unchecked, the battery at its end of life experiences a collapse in end of charge voltage, and may even go into thermal runaway. Once the end-of-charge voltage begins to crater, the battery life expectancy is short. Usage of the current interrupt (CI) technique forestalls the inevitable end of life. Nonetheless, there remains the difficult issue of finding an early predictor of battery life. This issue was studied under ALABC Project No. B-007.2. Data from two different algorithms, the Optima-recommended "normal charge" consisting of a constant voltage with a constant current overcharge (CV/CC), and a current interrupt (CI) charge were evaluated for signs of an early life predictor. An interesting pattern of an increase then drop in end-of-charge voltage accompanied by a surge then leveling out of capacity was identified 15% to 20% into the cycle life for both CV/CC and CI algorithms. The pattern proved predictive for the CV/CC cycle lives of several batteries, while the voltage surge as a predictor of CI cycle life depended completely on the specific algorithm. Characterization was also hampered by limited replicates. It is not known why this early voltage behavior occurs.