It develops voltage
It develops voltage from the chemical reaction produced when two unlike materials, such as the positive and negative plates, are immersed in the electrolyte, a solution of sulfuric acid and water. In a typical lead-acid battery, the voltage is approximately 2 volts per cell, for a total of 12 volts.
Battery acid is sulfuric acid that has been diluted with water to attain a 37% concentration level. This particular type of acid is used in sealed lead acid batteries, however, concentration levels differenciate with some brands.