Using thick grids, the life is extended because more grid must corrode before the battery fails. The rate of corrosion is related to the alloy of lead which is used. Calcium, antimony, and many other materials which are commonly used in lead acid cells greatly accelerate the rate of grid corrosion. Manufacturers use alloys such as these primarily because they add rigidity to the grids. Rigid grids are easy to handle through the manufacturing process.
Pure lead corrodes at a very slow rate compared to alloys of calcium and antimony.
High purity lead also minimizes the amount of hydrogen and oxygen gas which are generated from the electrolysis of water in the cell, preventing dry out. Using pure lead, it is possible to manufacture batteries with very thin electrodes which still have a long life. Thin electrodes result in improvements of active material utilization, especially when batteries are discharged at high rates. Using traditional alloys, it is possible to develop batteries with high power densities but short life, or batteries with long life but low power density. It is not possible to develop batteries which can deliver both.