atmospheric oxygen from entering the battery. The
1. Jar (monobloc). A container of suitable material
in which a single cell is assembled
valve allows small quantities of gas to escape when the
internal pressure exceeds the valve operating
2. Cell. A unit consisting of positive and negative
pressure.
plates, separators, a cell cover, and electrolyte, properly
assembled in a jar or one compartment of a monobloc
12. Positive terminal post. One of the two lead posts
case.
that protrude through the top of the battery. The point
at which the positive terminal connection is made to the
3. Element rest (bridge). The top surface of the
raised ribs forming the sediment spaces serves as the
external circuit.
base upon which the elements rest.
13. Positive plate strap. A piece of conductive
4. Plate feet. Projections at the bottom of the plates
material used to connect all the positive plates to a
(containing no active material). They serve as the point
common post through the top of the battery.
of contact between the elements and the bridge, or
14. Positive plate. One of the elements that makes
rest.
up the positive group of a battery. Consists of a plate of
5. Sediment space. A space formed by raised ribs
lead peroxide, PbO2 placed in a cell and submersed in
built into the bottom of a battery jar or monobloc case.
electrolyte.
This space serves as a receptacle for residue from the
element plates and separators. The residue is due to
SPECIFIC GRAVITY
deterioration caused by the chemical action between the
electrolyte and the plates across the separators. The
raised ribs also serve as baffles, preventing short circuits
The specific gravity of a liquid is the ratio of the
between the negative and positive plates by keeping the
weight of a certain volume of liquid to the weight of the
sediment from building up in any one area.
same volume of water is called the specific gravity of
the liquid Mathematically, this can be expressed as
6. Separator. Spacers placed between positive and
negative plates to prevent short circuiting. They maybe
follows:
made of wood or microporous rubber.
7. Rubber retainer. Sheets of suitable,
nonconductive material are used in conjunction with the
Where:
separators to help hold the active material of the positive
plates in place and to protect the separator from the
sp.gr. is the specific gravity
action of the positive material. They may be made of
hard rubber or synthetic compounds, perforated or
Wsample is the weight of a volume of the sample
slotted to allow free flow of the electrolyte.
being measured
8. Negative plate. One of the elements that makes
Wwater is the weight of the same volume of pure
up the negative group of a battery. Consists of a plate
water
of pure sponge lead (Pb) placed in a cell and submersed
The specific gravity of pure water is, by definition,
in electrolyte.
1.000. Sulfuric acid has a specific gravity of 1.830;
9. Negative plate strap. A piece of conductive
therefore, sulfuric acid is 1.830 times as heavy as water.
material used to connect all the negative plates to a
The specific gravity of a mixture of sulfuric acid and
common post through the top of the battery.
water varies with the strength of the solution from 1.000
10. Negative terminal post. One of the two lead
(pure water) to 1.830 (pure acid).
posts that protrude through the top of the battery. The
The electrolyte that is usually placed in a lead-acid
point at which the negative terminal connection is made
to the external circuit.
battery has a specific gravity of 1.350 or less. Generally,
the specific gravity of the electrolyte in standard storage
11. Vent plug (vented) or safety valve (sealed). In a
batteries (table 5-1) is adjusted between 1.210 and
vented battery, a threaded plug of suitable material with
1.220. However, the specific gravity of the electrolyte
a vent hole is used to prevent electrolyte from splashing
in batteries varies according to their intended
out of the cell but still allow gases to escape. Sealed
use.
batteries use a one-way pressure valve to prevent
5-2
