Section Ill. BASIC BATTERY OPERATING PRINCIPLES

TM 9-6140-200-14

Section Ill. BASIC BATTERY OPERATING PRINCIPLES

1-8. Battery Operation.

Lead-acid storage batteries consist of a number of identical cells. These cells contain

two different lead plates. These plates are immersed in electrolyte (a solution of

sulfuric acid and water). As the battery cell receives electrical energy (charges) or

delivers electrical energy (discharges), there is a change in the chemical composition

of the battery plates and the strength of the electrolyte. The voltage developed

depends on the types of electrode materials and the electrolyte used. It is

approximately 2.1 volts per cell in a typical lead-acid battery. Electrical energy is

produced by the chemical action between the electrode materials and the electrolyte.

The chemical actions start and electrical energy current flows from the battery as soon

as there is a circuit between the positive and negative terminals (whenever a load such

as the headlamps is connected to the battery). The electrical current flows as electrons

through the outside circuit, as it does inside the battery.

1-9. When the Battery Discharges.

a. When an external circuit is completed, such as turning on the ignition starting an

engine or turning on equipment lights, the lead-acid battery begins to discharge.

Discharge begins when the sulfuric acid in the electrolyte acts on lead peroxide in the

positive plates and the lead in the negative plates to form a new compound called lead

sulfate. The sulfations are supplied by the electrolyte, which becomes weaker in

concentration as discharge continues.

The decreased strength of the electrolyte is in direct proportion to the amount of

electricity taken from the battery cells. When the sulfate in the electrolyte is used up,

the battery stops producing (electricity) and it discharges (See Figure 1-2).

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