The effects of cell configuration and scaling factors on constant current discharge and dynamic charge acceptance in lead-acid batteries

Abstract

The active materials of batteries are often tested and selected at the cell level, which prevents comparability to battery-level performance. In the case of a typical lead-acid battery used in a vehicle, the performance after a few months in operation is not necessarily the same as it was during cell-level tests. The goal of this manuscript is to outline the most common reasons for the divergence in test results between cell-level tests and commercial batteries with respect to dynamic charge acceptance (DCA). To do so, this study tested 12 V-70 Ah enhanced flooded batteries (EFB) for their DCA properties. Afterwards, these batteries were dissembled to extract three 2 V test cells, some with a lower number of plates (3P2N and 2P1N). The aim of this investigation was to determine how the DCA of the original battery was affected by changing the plate count and the ratio between the positive active mass, the negative active mass, and the electrolyte by using industrially manufactured cell components – rather than introducing sources of errors by using handmade cells. Both the test batteries and the test cells were subjected to two different constant current discharge tests: the reserve capacity (RC) test and the C20 test. The DCA test according to Japanese Standard SBA S0101 2014 was also conducted. It was particularly important to identify operational conditions and scaling factors (e.g. voltages, currents, and acid densities) on the cell level – for cells with and without lower plate counts. Currently, these are only defined for battery testing according to standard test procedures. Our test cell design, with a reduced, asymmetric set of plates, generated an acid surplus and a PAM surplus, which in turn had major effects on steady-state properties such as the constant current discharge (as the RC test and C20 test showed). DCA battery and cell-level results are not comparable in terms of absolute values, especially for cells with lower plate count. The DCA results for single cells are systematically better for a lower plate count, which may be attributed to excess acid volume.