It must act as a capacitor (voltage stabilizer) that
smoothes current flow through the electrical
It must store energy (electricity) for extended
The type of battery used in automotive,
construction, and weight-handling equipment is a
lead-acid cell-type battery. This type of battery
produces direct current (dc) electricity that flows in
only one direction. When the battery is discharging
(current flowing out of the battery), it changes
chemical energy into electrical energy, thereby,
releasing stored energy. During charging (current
flowing into the battery from the charging system),
electrical energy is converted into chemical energy.
The battery can then store energy until the vehicle
The lead-acid cell-type storage battery is built to
withstand severe vibration, cold weather, engine heat,
corrosive chemicals, high current discharge, and
prolonged periods without use. To test and service
batteries properly, you must understand battery
construction. The construction of a basic lead-acid
cell-type battery is as follows:
Battery case, cover, and caps
BATTERY ELEMENT.The battery element is
made up of negative plates, positive plates, separators,
and straps (fig. 2-3). The element fits into a cell
compartment in the battery case. Most automotive
batteries have six elements.
Figure 2-3.Battery element.
Each cell compartment contains two kinds of
chemically active lead plates, known as positive and
negative plates. The battery plates are made of GRID
(stiff mesh framework) coated with porous lead. These
plates are insulated from each other by suitable
separators and are submerged in a sulfuric acid
Charged negative plates contain spongy (porous)
lead (Pb) which is gray in color. Charged positive
plates contain lead peroxide (PbO2) which has a
chocolate brown color. These substances are known as
the active materials of the plates. Calcium or antimony
is normally added to the lead to increase battery
performance and to decrease gassing (acid fumes
formed during chemical reaction). Since the lead on
the plates is porous like a sponge, the battery acid
easily penetrates into the material. This aids the
chemical reaction and the production of electricity.
Lead battery straps or connectors run along the
upper portion of the case to connect the plates. The
battery terminals (post or side terminals) are
constructed as part of one end of each strap.
To prevent the plates from touching each other and
causing a short circuit, sheets of insulating material
(microporous rubber, fibrous glass, or plastic-
impregnated material), called separators, are inserted
between the plates. These separators are thin and porous
so the electrolyte will flow easily between the plates.
The side of the separator that is placed against the
positive plate is grooved so the gas that forms during
charging will rise to the surface more readily. These
grooves also provide room for any material that flakes
from the plates to drop to the sediment space below.
BATTERY CASE, COYER, AND CAPS.The
battery case is made of hard rubber or a highquality
plastic. The case must withstand extreme vibration,
temperature change, and the corrosive action of the
electrolyte. The dividers in the case form individual
containers for each element. A container with its
element is one cell.
Stiff ridges or ribs are molded in the bottom of the
case to form a support for the plates and a sediment
recess for the flakes of active material that drop off the
plates during the life of the battery. The sediment is
thus kept clear of the plates so it will not cause a short
circuit across them.
The battery cover is made of the same material as
the container and is bonded to and seals the container.
The cover provides openings for the two battery posts
and a cap for each cell.