The lead-tin battery slowly lost capacity before leveling off at 96 percent of rated capacity on day 60. After 32 days, the lead-calcium batteries started to decline rapidly. After 80 days, the lead-calcium AGM produced at only 91 percent of rated capacity. The gel cell was down to 87 percent. One explanation for the accelerated energy loss is calcium-fostered corrosion of the positive electrode.
Pure lead corrodes very slowly compared to a lead-calcium alloy.
It also minimizes the amount of hydrogen and oxygen gas generated by electrolysis of water in the cell, preventing dry-out. Weight loss indicates that the battery is emitting gas and losing recombination efficiency. The lead-tin battery lost 29 grams. Similarly, as the grid corrodes, a battery's internal impedance increases, hindering energy flow within a battery and reducing capacity. Figure 5 shows changes in impedance for all three batteries during the accelerated temperature float test.