Lead-acid battery response to various formation levels - Part B: Internal resistance

In Part A of this study, eight lead-acid battery cells were formed to different levels to investigate their performance in conventional and off-grid solar photovoltaic applications. In Part B of the study (this article) the objective is to investigate the internal resistance of the cells as a function of finished formation level. Cells were formed to levels corresponding to 0.7, 1.4, 1.9, 2.3, 2.8, 4.2, 5.6, and 7.0 times their theoretical capacity, and cycled 10 times using a deep-cycle algorithm. A correlation between formation level and internal resistance is shown. Higher formation levels resulted in lower internal resistance values for both discharging and charging processes, although they differed in magnitude. It is also shown that internal resistance values of the under-formed cells start converging with the remaining cells after 4 cycles as they complete their formation process. It is recommended that manufacturers of under-formed cells suggest higher voltage setpoints during the constant-voltage phase of the charge. This would overcome the high internal resistance limitations of these aforementioned cells, thus allowing for faster formation completion, while increasing their energy efficiency in deep-cycling operation.