Investigation on Operating Characteristics of Individual Cells in a Lead-Acid Battery Pack

Similar to series-connected batteries, series-connected cells in a battery pack also suffer from the perplexity of unbalanced voltage while charging or discharging processes, especially for lead-acid batteries. This paper is to study the impact on capacity reduction under different operation conditions, such as different float-charging voltages, different cut-off discharging voltages and even discharging to negative voltages. The results reveal that the health of battery cells is more significantly affected by float-charging voltage than by the discharging cut-off voltage. However, discharging a cell into exceedingly negative voltage incurs a destructive consequence. A bypass protection circuit is proposed to mitigate the deterioration rate of battery cells. Experimental results show that the capacity reduction rate can be decreased distinctly.