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Battery Basics : 

Battery Basics


THE AUTOMOTIVE BATTERY A lead-acid storage battery is an electrochemical device that produces voltage and delivers electrical current. The battery is the primary "source" of electrical energy used in vehicles today. It's important to remember that a battery does not store electricity, but rather it stores a series of chemicals, and through a chemical process electricity is produced. Basically, two different types of lead in an acid mixture react to produce an electrical pressure called voltage. This electrochemical reaction changes chemical energy to electrical energy and is the basis for all automotive batteries.


THE PURPOSE OF THE BATTERY ENGINE IS OFF: Electricity from the battery is used to operate lighting, accessories, or other electrical systems when the engine is not running. ENGINE IS STARTING: Electricity from the battery is used to operate the starter motor and to provide current for the ignition system during engine cranking. Starting the car is the battery's most important function. ENGINE IS RUNNING: Electricity from the battery may be needed to supplement the charging system when the vehicle's electrical load requirements exceed the charging system's ability to produce electricity. Both the battery and the alternator supply electricity when demand is high.


BATTERY CONSTRUCTION An automobile battery contains a diluted sulfuric acid electrolyte and positive and negative electrodes, in the form of several plates. Since the plates are made of lead or lead-derived materials, this type of battery is often called a lead acid battery. A battery is separated into several cells (usually six in the case of automobile batteries), and in each cell there are several battery elements, all bathed in the electrolyte solution.


CELL OPERATION Two dissimilar metals placed in an acid bath produce electrical potential across the poles. The cell produces voltage by a chemical reaction between the plates and the electrolyte. The positive plate is made of reddish-brown material such as Lead Dioxide (PBO2) while the negative plate is made of grayish material called Sponge Lead (PB). The acid bath is a mixture of sulfuric acid and water cell electrolyte. Together a cell element is formed

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BATTERY CELL ELEMENT The key to battery operation is the cell element. Positive plates and negative plates are each connected together by separate plate straps. These groups of positive and negative plates are then placed alternately, separated by micro-porous separators. Assembled together, the plates and separators form a battery cell element. Grouping the plates in this way serves to enlarge the surface area between the active materials and the electrolyte, thus allowing a greater amount of electricity to be supplied. In other words, the battery capacity is increased because of the increase in surface area. More plate surface area means the battery can deliver more current.

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Battery plates : 

Battery plates Battery plates are constructed of a lead alloy containing a percentage of either Antimony or Calcium. The plates are designed as a thin flat grid, grids crossing at right angles


TYPES OF BATTERIES Lead Antimony Lead Calcium Recombination (Gel Cell)


LEAD ANTIMONY Lead-Antimony Cast GridConventional Low-Maintenance batteries use grids of Lead-antimony which is readily available, inexpensive, easy to cast, and provide a rechargeable battery that offers optimum efficiency and low cost. Lead antimony is used in Low-Maintenance batteries. Such batteries are built to reduce internal heat and water loss. Battery construction provides a deeper well area to allow a slight water loss over the life of the battery. Under normal conditions, the addition of water should not be required.

Lead-Calcium Grid : 

Lead-Calcium Grid The maintenance-free batteries, such as Delco Freedom batteries, uses calcium. The lead-calcium grid is strong, more resistant to corrosion as well as overcharging, gassing, water usage, and self-discharge, all of which shorten battery life in conventional lead-acid batteries. Lead calcium is used in Maintenance Free batteries. Battery construction provides a deeper well area to allow a slight water loss over the life of the battery. No provision for adding water to the cells is provided because the battery is sealed.


ELECTROLYTE Battery electrolyte is a mixture of 64% distilled water (H20) and 36% sulfuric acid (SO4). Batteries today have an electrolyte with a specific gravity of 1.270 (at 20'C, 68'F) when fully charged. Specific Gravity is the weight of a given volume of liquid in comparison to the weight of the same volume of water. The higher the specific gravity of a liquid the denser (thicker) it is. Testing specific gravity will be discussed in the Battery Service Module.


BATTERY CASE The battery case holds the electrolyte and the individual battery cell elements. It is divided into six compartments or cells. The plates are raised up off the bottom of the case with ribs to prevent them from shorting out if any of the active materials (lead, etc.) should happen to fall from the plates. The case is made of polypropylene, hard rubber, and plastic base materials. Some battery manufacturers use translucent plastic cases which allow checking electrolyte level without removing vent caps. These cases often have "upper" and "lower" electrolyte level markers on the outside of the case.

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VENT CAPS Vent caps are used to cover the holes used for adding electrolyte. These caps are also designed to separate the sulfuric acid mist and the hydrogen gas that forms when the battery charges. This vent system allows sulfuric acid mist to condense and drop back into the battery and allow hydrogen gas to escape through the vent holes to the atmosphere.

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BATTERY TERMINAL DESIGN Three design types of battery terminals are used; the Top (Post) Terminal, Side Terminal, and the "L" Terminal types. The top terminal design is the most popular among automotive batteries. Top post terminal batteries have tapered posts on the top of the battery. The side terminal design is used exclusively by General Motors, and the "L" terminal design is used in marine applications; both have internally threaded terminals.


BATTERY TERMINAL IDENTIFICATION Battery terminals are identified as either "positive" or "negative". Battery cases are marked with a "+" for the positive terminal, and a "-" on the negative terminal The words "POS" or "NEG" are often used instead of the + or -. On top post terminal batteries, the positive post is slightly wider than the negative terminal post. This allow for easy identification.

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