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).
1-5
