Electrolyte

During the reactions of current generation and accumulation in the lead–acid battery, the concentration of H2SO4 in the electrolyte changes. The battery has the highest performance parameters when the changes in H2SO4 concentration on cycling are within the window from 1.10 to 1.28 specific gravity (SG). In this acid concentration window, lead dioxide has the highest electrochemical activity, lead sulfate is sufficient soluble, and the H2SO4 solution is most electroconductive. Acid concentration determines battery voltage, which should be taken into account when selecting the charge voltage so as to guarantee full charge of the battery. Battery performance depends on the utilization coefficients of the three active materials: Pb, PbO2, and H2SO4. When the H2SO4 utilization is higher than that of Pb and PbO2, the battery has lower initial capacity, but longer cycle life. When Pb and PbO2 are the capacity-limiting active materials, the initial capacity of the battery is high, but its cycle life is shorter.