Batteries transform chemical energy into electrical energy. Each battery contains multiple electric cells which in turn has two electrodes made from different chemically- active materials with positive and negative charges. Each cell contains an electrolyte that acts as a medium to conduct electric current within the cell. When the electrodes of a battery are connected to an electric circuit, current is produced.

There are two main functions of an automotive battery. It is a source of power supply for the vehicle's starter. The electrical power required to crank an engine varies from vehicle to vehicle, depending on the engine stroke and bore, the number of cylinders, starter cranking ratio, circuit resistance, temperature, engine oil viscosity and accessory load. All these factors form the main considerations in the original battery equipment specified by the automobile manufacturer.

Automotive battery also supplement the vehicle's load requirements in the event there is an excess demand on the delivery capabilities of the vehicle's charging system. Charging systems maintain the electrical loads under normal driving condition; however, if the engine is at an "idling" speed, the automotive battery will then have to supply a portion of the accessory load and also automatically supply the vehicle's electrical load in the event of failure in the charging systems.

The effectiveness of the lead-acid storage battery is determined by chemicals such as lead oxide (the material pasted on the positive grid), spongy lead (for the negative plate) and sulphuric acid (the medium for the electrolyte).