Today’s car batteries are built in some ways like batteries first used in the early years of the 20th century to start the early model cars in which they were first installed. The advent of the car battery allowed for the removal of the hand-cranked starter that would occasionally kick back or lurch, causing injury in many car owners of that time period. The design of the battery has a lengthy history, but its basic construction today makes it among the simplest, yet most-important, devices in your car.
Most car batteries are of the lead acid type and contain at least six compartments which are able to produce two volts of electricity each. This gives car batteries the common twelve volt designation we have become so accustomed to seeing in our cars. When you turn the ignition in your car, the small amount of electricity stored at this time is released and additional electricity is generated almost instantaneously as a chemical reaction occurs between the lead plates and the sulfuric acid found in each of the six compartments. The sulfuric acid is diluted with water and is an electrolyte that allows the free flow of electricity during the use of the battery.
The positive plates of the battery contain lead oxide while the negative plates contain pure lead. These plates are separated by sheets of material that keep the plates from directly contacting one another and short-circuiting within the battery. The positive plates are welded to the positive electrode while the negative plates are welded to the negative electrode. Each electrode passes through the top or side of the battery and they are clearly marked as “+” or “-“. Each electrode is attached to the car’s electrical system by a cable (red to positive and black to negative).
The outer case of the battery is made of polypropylene and moulded to fit the car for which it was designed. Batteries first produced in the early part of the 20th century had an outer housing made of hard ceramic and could easily be opened at the top. Opening the top of the battery allowed the car owner access to the solution inside the battery to add more water if it began to dry out. Today’s car batteries do not generally have such ease of access and in fact the manufacturers of these batteries ask consumers to not attempt to open them. Replacement is best, with the old battery returned to the retailer for recycling.