When two unlike materials such as the positive and negative plates are immersed in sulfuric acid (electrolyte), a battery is created and voltage is developed. The amount of voltage developed depends on the types of materials used in the plates and the electrolyte used. The voltage is approximately 2.1 volts per cell in a typical lead-acid battery. Electrical energy is produced by the chemical reaction between the different materials and the electrolyte. When the chemical reaction starts, electrical energy flows from the battery as soon as there is a circuit between the positive and negative terminals. Inside the battery, the electrical current flows as electrons through the outside circuit, and as charged ions between the plates.

What is the Purpose of a Battery?
There are three main functions of the automotive battery. The main function for most vehicle batteries is to supply power the starter and ignition system so the engine can be cranked or started. The second is to supply the extra power necessary when the vehicle’s electrical load requirements exceed the supply from the charging system. The battery must also act as a voltage stabilizer in the electrical system. The battery smoothes out or reduces high voltages, which occur in the vehicle’s electrical system. These excessively high voltages would damage other components in the electrical system if it were not for the protection provided by the battery.

How does a Battery Recharge?
The discharged material on both plates is lead sulfate (PbSO4). When a charging voltage is applied, charge flow occurs. Electrons move in the metal parts; ions and water molecules move in the electrolyte. Chemical reactions occur at both the positive and negative plates converting the discharged material into charged material. The material on the positive plate is converted to lead dioxide (Pb02); the material on the negative plate is converted to lead (Pb). Sulfuric acid is produced at both plates and water is consumed at the positive plate.