Battery An automobile battery is essentially a 12 volt wet cell battery. Wet cell batteries consist of lead plated immersed in an acid solution such that current is generated between the plates. This current is then run to the electrical system of the vehicle through a positive and negative terminal. The negative is usually attached directly to the frame to serve as a negative ground for the system to simplify wiring. The battery's main function is to operate the starter motor. Once the vehicle is started, the alternator takes over the major electrical duties. If the alternator cannot supply enough current or the engine is not running, the battery atts supplemental current to the circuit.