GMC 1976 ZEO 6083 Maintenance Manual page 383

Figure 5-Maintenance-Free Battery
MAINTENANCE FREE BATTERIES
The maintenance-free batteries are identified by
the absence of vent plugs on the cover (figure 5) . The
battery is completely sealed except for small vent
holes on the sides. These vent holes allow what small
amount of gases are produced in the battery to es-
cape . The special chemical composition in the bat-
tery grid design reduces the production of gas to an
extremely small amount at normal charging volt-
ages . Water never needs to be added to the mainte-
nance-free battery. A charge indicator in the cover
indicates state of charge . This feature is discussed
later in this section under "Charging Guide" .
GENERAL DESCRIPTION
The battery is made up of a number of separate
elements, each located in an individual cell in a hard
rubber case . Each element consists of an assembly of
positive plates and negative plates containing dis-
similar active materials and kept apart by separators .
In the maintenance-free battery these separators are
replaced with negative plate envelopes. The elements
are immersed in an electrolyte composed of dilute
sulfuric acid . Plate straps located on the top of each
element connect all the positive plates and all the
negative plates into groups .
The elements are connected in series electrically by
connectors that pass directly through the case parti-
tions between cells. The battery top is a one piece
cover. The cell connectors, by passing through the
cell partitions, connect the elements along the short-
ENGINE ELECTRICAL 6Y- 3
est practical path (figure 6) . With the length of the
electrical circuit inside the battery reduced to a mini-
mum, the internal voltage drop is decreased resulting
in improved performance, particularly during engine
cranking at low temperatures .
The terminals of this type battery, passing
through the side of the case, are positioned out of the
"wet" area surrounding the vent wells. Normal spil
lage, spewing, condensation and road splash are not
as likely to reach or remain on the vertical sides
where the terminals are located. This greatly de-
creases the cause of terminal corrosion. Also, con-
struction of the terminals is such that the mating
cable connector seals the junction and provides a
permanently tight and clean connection . Power rob-
bing resistance in the form of corrosion is thereby
eliminated at these maintenance-free connections.
The hard, smooth, one piece cover greatly
reduces the tendency for corrosion to form on the top
of the battery. The cover is bonded to the case form-
ing an air-tight seal between the cover and case .
Electrical energy is released by chemical reac-
tions between the active materials in the two dissimi-
lar plates and the electrolyte whenever the battery is
being "discharged." Maximum electrical energy is
released only when the cells are being discharged
from a state of full charge .
As the cells discharge, chemical changes in the
active materials in the plates gradually reduce the
potential electrical energy available. "Recharging"
the battery with a flow of direct current opposite to
that during discharge reverses the chemical changes
within the cells and restores them to their active
condition and a state of full charge .
Th6re are two types of batteries, the "dry charge"
type and the "wet charge" type . The difference in
types depends on the method of manufacture. A "dry
charge" battery contains fully charged elements
which have been thoroughly washed and dried. This
type of battery contains no electrolyte until it is ac-
tivated for service in the field and, therefore, leaves
the factory in a dry state. Consequently, it is called
a "dry charge" battery.
Each vent well in a "dry charge" battery has a
hard rubber seal to prevent the entrance of air and
moisture which would oxidize the negative active
materials and reduce the freshness of the battery
(figure 7) . The hard rubber seals and the bonding
between the case and one-piece cell cover make poss-
ible a vacuum sealed assembly which can be stored
for very long periods of time without detrimental
effects.
Before activating the "dry charge" battery, the
hard rubber seals are broken simply by pushing the