Batteries are provided with side, top stud and top post
type terminals (Figure 3) for various vehicle
Figure 3 - Types of Battery Terminals
LOW MAINTENANCE BATTERIES
These are conventionally vented lead-acid batteries
requiring normal periodic battery maintenance.
A small amount of antimony has been added to the lead
to improve grid strength. The antimony tends to cause
"gassing" (breaking down of water into hydrogen and
oxygen gases) during battery operation, thereby lowering
the electrolyte level. Hence, periodic addition of water to
the battery cells is required.
"Fleetrite" and "International" low maintenance batteries
are provided with easily accessible cell filler caps.
MAINTENANCE FREE BATTERIES
Maintenance free batteries do not require the addition of
water during normal service life. This is due to the fact
that maintenance free batteries utilize calcium rather
than antimony to improve grid strength. The advantage
of calcium is that it greatly reduces the tendency for the
battery to gas at normal charging voltages.
Consequently, very little water is used.
Maintenance free batteries are not sealed. All batteries
(including maintenance free) generate gases, especially
during charge. While the volume of gases produced by
the maintenance free battery is reduced by more than
75%, there are small vent openings to allow this gas to
escape of the battery is turned upside down or placed on
"Fleetrite" and "International" maintenance free batteries
have concealed cell caps which can be removed to
permit battery testing and addition of water if required.
ELECTROLYTE AND SPECIFIC
The electrolyte in a lead-acid storage battery is a dilute
sulfuric acid solution. The sulfuric acid in the electrolyte
is one of the necessary ingredients in the chemical
actions taking place inside the battery. It supplies the
sulfate which combines with the active material of the
plates. It is also the carrier for the electric current as it
passes from plate to plate. When the battery terminals
are connected to an external load, the sulfate combines
with the active materials of the positive and negative
plates forming lead sulfate and releasing electrical
Specific gravity is a unit of measurement for determining
the sulfuric acid content of the electrolyte. The
recommended fully charged specific gravity of most 12-
volt batteries today is 1.265 corrected to 26.7oC 80°F). A
battery with a fully charged specific gravity of 1.265
contains an electrolyte with approximately 36% sulfuric
acid by weight or 25% by volume. The remainder of the
electrolyte is water. Pure (concentrated) sulfuric acid
has a specific gravity of 1.835. Water has been
assigned a value of 1.000. Therefore, electrolyte with a
specific gravity of 1.265 means it is 1.265 times heavier
than pure water.
The state-of-charge of a battery can be determined by
the specific gravity of the electrolyte. The specific gravity
can be measured directly with a hydrometer (Figure 4).
A hydrometer is a bulb-type syringe which will extract
electrolyte from the cell. A glass float in the hydrometer
barrel is calibrated to read in terms of specific gravity.
The lower the float sinks in the electrolyte, the lower its
Figure 4 - Battery Hydrometer
Figure 5 graphically illustrates the relationship between
gravity readings and the combination of the sulfate from
the acid with the positive and negative plates for various
states of charge. The black dots represent the sulfate
radical. A fully charged battery has all of the sulfate in
the acid. As the battery discharges, some of the sulfate
begins to appear on the plates. The acid becomes more
dilute and its specific gravity drops as water replaces
some of the sulfuric acid. A fully discharged battery has
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