Battery Principles

What is a Battery? An automotive battery is an electrochemical device that produces and stores electricity. A battery only produces direct current DC electricity. When discharging (current flows out of the battery), the battery changes chemical energy into electrical energy. In this way it releases stored energy.

During charging (current flowing into the battery from the charging system) electrical energy is converted into chemical energy. The battery can store this energy until needed.

Battery Cell A simple battery cell has a negative plate, positive plate, container, and electrolyte (battery acid).

Battery Cell Action When the cell is being charged, the alternator causes free electrons (negative charges) to be deposited on the negative plates. This causes the plates to have a difference in potential (electrical pressure, or voltage). When a load is connected across the terminals, there is a current flow of electrons to equalize the difference in charges on the plates. The excess electrons move from the negative plate to the positive plate.

Battery Function A vehicle battery has several important functions,It must: Operate the starter motor, ignition system, fuel system. Supply all electrical power when the engine is not running. Help the charging system provide electricity when current demands exceed the output limit of the charging system. Act as a capacitor that smoothes current flow. Stores energy (electricity)

Battery Construction Batteries are built to withstand sever vibration, extreme temperature, corrosive chemicals, high current discharge, and prolonged periods without use. Battery element- is made up of positive plates, negative plates, straps, and separators. The element fits into the cell compartment in the case. Battery plates- are made of a grid (stiff mesh) coated with porous lead.

The chemically active material in the negative plates is porous lead The chemically active material in the negative plates is porous lead. The active material on the positive plate is lead peroxide. Calcium is normally added to the lead to increase battery performance and to decrease gassing (acid fumes forming during chemical reaction).

Electrolyte Battery Acid (electrolyte) - is a mixture of sulfuric acid and distilled water. Electrolyte is poured into each cell until the plates are covered. Distilled water is used because it does not contain impurities found in tap water. This will prolong the battery life.

Battery charge indicator Also called the battery eye or test indicator shows the general state of charge of the battery. It gives a reading of the cell that it is located over. The charge indicator changes color as the level of battery charge changes. Usually green eye indicates full charge, black when discharged, yellow when the battery needs replacement.

Battery Voltage- battery open voltage (no load) cell voltage is 2 Battery Voltage- battery open voltage (no load) cell voltage is 2.1 volts, since the cells in a battery are connected in series. Battery voltage depends on the number of cells. 12 volt battery has 6 cells which produce an open circuit voltage of 12.6 volts. Modern Vehicles use a 12 volt system older vehicles and farm equipment use a 6 volt system. Off road and motorcycle also can work off 6 volts it is important to know the type of system being serviced.

Battery Cables They are large gauge cables that connect the battery to the vehicles electrical system. The positive cable is normally red and fastens to the starter solenoid. The negative battery cable is black and connects to ground on the engine block.

Battery rating C.C.A. - determines how much current (amps) the battery can deliver for 30 seconds at 0◦F while maintaining terminal voltage of 7.2 volts. Reserve capacity- is the time needed to lower battery terminal voltage below 10.2 volts. Reserve capacity will be given a time rating e.g. 90 min reserve capacity. If the charging system fails the driver can travel for 90 minutes under minimal electrical loads (headlights off, heater fan off) before the battery goes completely dead and the engine shuts off.

Battery and Temperature As the battery temperature drops, battery power is reduced. At lower temperatures, the chemical reaction inside the battery is slowed. This affects a batteries ability to start an engine in extremely cold weather.

Parasitic Load Includes any current draw present when all electrical devices are shut off. E.g. dash board clock, on board computers these all need small current to maintain there memory. This is a parasitic load and prolonged periods of a vehicle sitting can drain the battery enough to prevent starting.

Sulfated battery Lead sulfate that exists when a battery is not fully charged crystallizes to become a hard lead sulfate when left in a battery for a period of time. During the normal discharge process, lead and sulfur combine into soft lead sulfate crystals formed in the pores and on the surfaces of the positive and negative plates inside a lead-acid battery. The soft lead sulfate re-crystallizes into hard lead sulfate

Removing a battery To remove a battery from a vehicle it is important to follow these safety steps. Always wear safety glasses, use an open end wrench, disconnect the negative lead first then disconnect the positive lead, unscrew the battery hold down clamp and remove the battery. When installing a battery reverse the procedure, positive first then negative. Note it is a good idea to install a memory saver before the battery is disconnected so the vehicles drive cycle, clock, radio presets are not disrupted.