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. The lead-tin battery began with an impedance of 2.4 milliohms and never increased. The lead-calcium AGM battery started with 3.5 milliohms and remained constant.