The lead–acid battery is one of the most successful electrochemical systems and the most successful storage battery developed. The lead–acid battery consists of a number of cells in a container. These cells contain positive (PbO
2
) and negative (Pb) electrodes or plates, separators to keep the plates apart, and sulfuric acid, H
2
SO
4
, electrolyte. The battery reactions are highly reversible, so that the battery can be discharged and charged repeatedly. Each cell has a nominal voltage of 2 V and capacities typically vary from 1 to 2000 ampere‐hours. The many cell designs available for a wide variety of uses can be divided into three main categories: automotive, industrial, and consumer. Automotive batteries as a category constitute starting, lighting, and ignition (SLI) for cranking of internal combustion engines battery sales. Industrial batteries are used for heavy‐duty application such as motive and standby power. More recently, the use of batteries for utility peak shaving has been increasing. Consumer batteries are used for emergency lighting, security alarm systems, cordless convenience devices and power tools, and small engine starting. This is one of the fastest growing markets for the lead–acid battery. Automotive and industrial motive power batteries have the standard free electrolyte systems and operate only in the vertical position. Two types of batteries having immobilized electrolyte systems are also made. They are most common in consumer applications, but their use in industrial and SLI applications is increasing. They are sometimes called valve regulated or recombinant batteries because they are equipped with a one‐way pressure relief vent and normally operate in a sealed condition. In the gelled electrolyte battery, the sulfuric acid electrolyte has been immobilized by a thixotropic gel. Other cells use a highly absorbent separator to immobilize the electrolyte. The double sulfate theory has been confirmed by a number of methods as the only reaction consistent with the lead–acid battery system. Lead sulfate is formed as the battery discharges, and sulfuric acid is regenerated as the battery is charged. The open circuit voltage of the lead–acid battery is the function of the acid concentration and temperature. The battery voltage is obtained by multiplying the cell voltage by the number of cells. The corrosion of the lead grid at the lead dioxide electrode is one of the primary causes of lead–acid battery failure. At high discharge rates, such as those required for starting an engine, the voltage of the lead–acid battery drops sharply, primarily because of the resistance of the lead current collectors. This voltage drop increases with the cell height and becomes significant even at moderate discharge rates in large industrial cells. Researchers have developed a model which has been used to improve grid designs for automotive batteries. The shelf life of the lead–acid battery is limited by self‐discharge reactions. High temperatures reduce shelf life significantly. The lead–acid battery is comprised of three primary components: the element, the container, and the electrolyte. The element consists of positive and negative plates connected in parallel and electrically insulating separators between them. The container is the package which holds the electrochemically active ingredients and houses the external connections or terminals of the battery. The electrolyte, which is the liquid active material and ionic conductor, is an aqueous solution of sulfuric acid. Whereas automotive batteries have the majority of the market, other types of lead–acid batteries are making inroads into various applications. The automotive battery's operating environment has changed substantially in the last 10 years. Underhood temperature has risen and electrical loads have increased. Battery design is changing to meet these needs.
