General Information; Description And Operation; Battery Size And Ratings; Battery - Jeep 1996 Grand Cherokee Service Manual

8A - 2

BATTERY

GENERAL INFORMATION (Continued)
condition. See Built-In Test Indicator in this group
for more information.
It is important that the battery, starting, and
charging systems be thoroughly tested and inspected
any time a battery needs to be charged or replaced.
The cause of abnormal discharge, over-charging, or
early battery failure must be diagnosed and corrected
before a battery is replaced or returned to service.

DESCRIPTION AND OPERATION

BATTERY
The storage battery is a device used to store elec-
trical energy potential in a chemical form. When an
electrical load is applied to the battery terminals, an
electrochemical reaction occurs within the battery.
This reaction causes the battery to discharge electri-
cal current.
The battery is made up of six individual cells that
are connected in series. Each cell contains positively
charged plate groups made of lead oxide, and nega-
tively charged plate groups made of sponge lead.
These dissimilar metal plates are submerged in a
sulfuric acid and water solution called an electrolyte.
As the battery discharges, a gradual chemical
change takes place within each cell. The sulfuric acid
in the electrolyte combines with the plate materials,
causing both plates to slowly change to lead sulfate.
At the same time, oxygen from the positive plate
material combines with hydrogen from the sulfuric
acid, causing the electrolyte to become mainly water.
The chemical changes within the battery are
caused by the movement of excess, or free, electrons
between the positive and negative plate groups. This
movement of electrons produces a flow of electrical
current through the load device attached to the bat-
tery terminals.
As the plate materials become more similar chem-
ically, and the electrolyte becomes less acid, the volt-
age potential of each cell is reduced. However, by
charging the battery with a voltage higher than that
of the battery, the battery discharging process is
reversed.
Charging the battery gradually changes the sul-
fated lead plates back into sponge lead and lead
oxide, and the water back into sulfuric acid. This
action restores the difference in the electron charges
deposited on the plates, and the voltage potential of
the battery cells.
For a battery to remain useful, it must be able to
produce high-amperage current over an extended
period. A battery must also be able to accept a
charge, so that its voltage potential may be restored.
In addition to producing and storing electrical
energy, the battery serves as a capacitor, or voltage
stabilizer, for a vehicle's electrical system. It absorbs
most abnormal or transient voltages caused by the
switching of any of the vehicle's electrical compo-
nents.
The battery is vented to release excess hydrogen
gas that is created when the battery is being charged
or discharged. However, even with these vents, the
hydrogen gas can collect in or around the battery. If
hydrogen gas is exposed to flame or sparks, it may
ignite.
If the electrolyte level is low, the battery may arc
internally and explode. If the battery is equipped
with removable cell caps, add distilled water when-
ever the electrolyte level is below the top of the
plates. If the battery cell caps cannot be removed, the
battery must be replaced if the electrolyte level
becomes low.

BATTERY SIZE AND RATINGS

The outside dimensions and terminal placement of
the battery conform to standards established by the
Battery Council International (BCI). Each battery is
assigned a BCI Group Size number to help identify a
correctly-sized replacement.
In addition, there are two commonly accepted
methods for rating and comparing battery perfor-
mance. These ratings are called Cold Cranking
Amperage (CCA) and Reserve Capacity (RC). Both
ratings are described in more detail below.
The Group Size number, CCA rating, and RC rat-
ing can be found on the original equipment battery
label. Be certain that a replacement battery has the
correct Group Size number, as well as CCA and RC
ratings that equal or exceed the original equipment
specification for the vehicle being serviced. See the
Battery Classifications and Ratings chart in Specifi-
cations at the back of this group for more informa-
tion.
COLD CRANKING AMPERAGE
The Cold Cranking Amperage (CCA) rating speci-
fies how much current (in amperes) the battery can
deliver for 30 seconds at -17.7°C (0°F). Terminal volt-
age must not fall below 7.2 volts during or after the
30 second discharge. The CCA required is generally
higher as engine displacement increases, depending
also upon the starter current draw requirements.
RESERVE CAPACITY
The Reserve Capacity (RC) rating specifies the
time (in minutes) it takes for battery terminal volt-
age to fall below 10.2 volts, at a discharge rate of 25
amperes. RC is determined with the battery fully-
charged at 26.7°C (80°F). This rating estimates how
long the battery might last after a charging system
failure, under minimum electrical load.
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