An automotive battery (Figure 5-1) is an electrochemical device capable of storing and producing electrical energy. Electrochemical refers to the chemical reaction of two dissimilar materials in a chemical solution that results in electrical current. When the battery is connected to an external load, such as a starter motor, an energy conversion occurs that results in an electrical current fl owing through the circuit. Electrical energy is produced in the battery by the chemical reaction that occurs between two dissimilar plates that are immersed in an electrolyte solution.
Activation of the battery is through the addition of electrolyte. Th is solution causes the chemical actions to take place between the lead peroxide of the positive plates and the sponge lead of the negative plates. The electrolyte is also the carrier that moves electric current between the positive and negative plates through the separators.
In a maintenance-free battery there is no provision for the addition of water to the cells. The battery is sealed. It (Figure 5-10) contains cell plates made of a slightly different compound than what is in a conventional battery. The plate grids contain calcium, cadmium, or strontium to reduce gassing and self-discharge. Gassing is the conversion of the battery water into hydrogen and oxygen gas.
A recent variation of the automobile battery is the recombination battery (Figure 5-17). The recombination battery is sometimes called a gel-cell battery. It does not use a liquid electrolyte. Instead, it uses separators that hold a gel-type material. Th e separators are placed between the grids and have very low electrical resistance. The spiral design provides a larger plate surface area than that in conventional batteries.
The battery that is selected should fi t the battery holding fixture and the hold-down must be able to be installed. It is also important that the height of the battery not allow the terminals to short across the vehicle hood when it is shut. BCI group numbers are used to indicate the physical size and other features of the battery. This is group number does not indicate the current capacity of the battery.