Lead-Acid Cranking Battery Basics


I. How a battery works
A. A lead storage cell is the most common type of storage cell used. It is basically a prepackaged, reversible chemical reaction. Its primary components are a positive terminal connected to plates made of PbO2 (lead dioxide) and a negative terminal connected to plates made of spongy metal lead (Pb) with both sets of plates saturated in an electrolyte solution of 33% sulfuric acid (H2SO4).
B. When an electrical circuit is made between the positive and negative terminals, the sulfuric acid is allowed to react with the lead on the negative plate to form lead dioxide (PbO2) and water (H2O) plus sulfur (S). Electrons have to be jettisoned to allow this reaction to drive forward. At the same time the sulfuric acid reacts with the lead dioxide on the positive plate to form lead sulfate.
C. When the terminal voltage is increased with a rectifier or other power source and electrons are forced back into the cell, the reaction is reversed, reforming the original lead dioxide on the positive plates, metal lead on the negative plates and sulfuric acid in the solution.

A battery stores energy, not electricity.
II. Care and maintenance
A. A battery should always be fresh. Since it is a chemical reaction, it begins to deteriorate as soon as it is manufactured. Although there may be exceptions, the maximum life of a cranking battery is usually three years, after this loss of capacity begins to affect performance.
B. A battery should be stored at about 70 degrees Fahrenheit. Significant variations in temperature, during storage, may affect capacity. The battery may be used in a wide variety of temperature ranges, however, so long as it is kept charged. A discharged battery will freeze.
C. A 12 volt battery should be float charged at 12.75 to 13 volts. Higher float voltages will damage the battery and lower voltages may not maintain full charge. (25.5 to 26 volts for a system using two 12 volt batteries in series.)
D. A battery charging alternator, driven by the engine, should not exceed 14 volts. (28 volts for a system using two 12 volt batteries in series.) Measure this voltage with the engine running.
E. Always keep the battery case clean. An electrical path may develop between the posts of a dirty battery, causing discharge.
F. Never allow a battery to remain discharged. A battery is a packaged chemical reaction. The lead sulfate that develops as a part of the discharge process will not be reversible if the battery is not recharged immediately.
G. If a battery is dropped or jarred, plates may break loose inside. The battery should always be secured and kept away from vibration if possible.

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