Jeep Grand Cherokee WJ. Manual - part 81

Battery Diagnosis

Condition

Possible Causes

Correction

The battery state-of-charge
cannot be maintained.

1. The battery has an
incorrect size or rating for
this vehicle.
2. The battery terminal
connections are loose or
corroded.
3. The generator drive belt is
slipping.
4. The electrical system
ignition-off draw is excessive.
5. The battery is faulty.
6. The starting system is
faulty.
7. The charging system is
faulty.
8. Electrical loads exceed the
output of the charging
system.
9. Slow driving or prolonged
idling with high-amperage
draw systems in use.

1. Refer to Battery in the index of this service
manual for the location of the proper battery
specifications. Replace an incorrect battery, as
required.
2. Refer to Voltage Drop Test in this section for
the proper test procedures. Clean and tighten the
battery terminal connections, as required.
3. Refer to Accessory Drive Belt Diagnosis in the
index of this service manual for the location of the
proper accessory drive belt diagnosis and testing
procedures. Replace or adjust the faulty
generator drive belt, as required.
4. Refer to Ignition-Off Draw Test in this section
for the proper test procedures. Repair the faulty
electrical system, as required.
5. Determine the battery cranking capacity. Refer
to Load Test in this section for the proper test
procedures. Replace the faulty battery, as
required.
6. Determine if the starting system is performing
to specifications. Refer to Starting System in the
index of this service manual for the location of the
proper starting system diagnosis and testing
procedures. Repair the faulty starting system, as
required.
7. Determine if the charging system is performing
to specifications. Refer to Charging System in the
index of this service manual for the location of the
proper charging system diagnosis and testing
procedures. Repair the faulty charging system, as
required.
8. Inspect the vehicle for aftermarket electrical
equipment which might cause excessive electrical
loads.
9. Advise the vehicle operator, as required.

The battery will not accept a
charge.

1. The battery is faulty.

1. Refer to Battery Charging in the index of this
service manual for the location of the proper
battery charging procedures. Charge or replace
the faulty battery, as required.

ABNORMAL BATTERY DISCHARGING

Any of the following conditions can result in abnor-

mal battery discharging:

1. Corroded or loose battery posts and terminal

clamps.

2. A loose or worn generator drive belt.
3. Electrical loads that exceed the output of the

charging system. This can be due to equipment installed
after manufacture, or repeated short trip use.

4. Slow driving speeds (heavy traffic conditions) or

prolonged idling, with high-amperage draw systems
in use.

5. A faulty circuit or component causing excessive

ignition-off draw.

6. A faulty or incorrect charging system compo-

nent. Refer to Charging System in the index of this
service manual for the location of the proper charg-
ing system diagnosis and testing procedures.

7. A faulty or incorrect starting system component.

Refer to Starting System in the index of this ser-
vice manual for the location of the proper starting
system diagnosis and testing procedures.

8. A faulty or incorrect battery.

8A - 8

BATTERY

DIAGNOSIS AND TESTING (Continued)

TESTING

BUILT-IN TEST INDICATOR

A test indicator (hydrometer) built into the top of

the battery case provides visual information for bat-
tery testing (Fig. 7). Like a hydrometer, the built-in
test indicator measures the specific gravity of the
battery electrolyte. The test indicator reveals the bat-
tery state-of-charge; however, it will not reveal the
cranking capacity of the battery. A load test must be
performed to determine the battery cranking capac-
ity. Refer to Load Test in this section for the proper
battery load testing procedures.

WARNING:

•

IF THE BATTERY SHOWS SIGNS OF FREEZ-

ING, LEAKING, LOOSE POSTS, OR LOW ELECTRO-
LYTE LEVEL, DO NOT TEST, ASSIST-BOOST, OR
CHARGE. THE BATTERY MAY ARC INTERNALLY
AND EXPLODE. PERSONAL INJURY AND/OR VEHI-
CLE DAMAGE MAY RESULT.

•

EXPLOSIVE HYDROGEN GAS FORMS IN AND

AROUND THE BATTERY. DO NOT SMOKE, USE
FLAME, OR CREATE SPARKS NEAR THE BATTERY.
PERSONAL INJURY AND/OR VEHICLE DAMAGE
MAY RESULT.

•

THE BATTERY CONTAINS SULFURIC ACID,

WHICH IS POISONOUS AND CAUSTIC. AVOID CON-
TACT WITH THE SKIN, EYES, OR CLOTHING. IN
THE EVENT OF CONTACT, FLUSH WITH WATER
AND CALL A PHYSICIAN IMMEDIATELY. KEEP OUT
OF THE REACH OF CHILDREN.

•

IF THE BATTERY IS EQUIPPED WITH REMOV-

ABLE CELL CAPS, BE CERTAIN THAT EACH OF
THE CELL CAPS IS IN PLACE AND TIGHT BEFORE
THE BATTERY IS RETURNED TO SERVICE. PER-
SONAL INJURY AND/OR VEHICLE DAMAGE MAY
RESULT FROM LOOSE OR MISSING CELL CAPS.

Before testing, visually inspect the battery for any

damage (a cracked case or cover, loose posts, etc.)
that would cause the battery to be faulty. In order to
obtain correct indications from the built-in test indi-
cator, it is important that the battery be level and
have a clean sight glass. Additional light may be
required to view the indicator. Do not use open
flame as a source of additional light.

To read the built-in test indicator, look into the

sight glass and note the color of the indicator (Fig. 8).
The battery condition that each color indicates is
described in the following list:

• Green

Indicates 75% to 100% battery state-of-charge. The
battery is adequately charged for further testing or
return to service. If the starter will not crank for a
minimum of fifteen seconds with a fully-charged bat-
tery, the battery must be load tested. Refer to Load
Test in this section for the proper battery load test-
ing procedures.

• Black or Dark

Indicates 0% to 75% battery state-of-charge. The bat-
tery is inadequately charged and must be charged
until a green indication is visible in the sight glass
(12.4 volts or more), before the battery is tested fur-
ther or returned to service. Refer to Battery Charg-
ing in the index of this service manual for the
location of the proper battery charging procedures.
Also refer to Abnormal Battery Discharging in
this section for the possible causes of the discharged
battery condition.

• Clear or Bright

Indicates a low battery electrolyte level. The electro-
lyte level in the battery is below the test indicator. A
maintenance-free battery with non-removable cell
caps must be replaced if the electrolyte level is low.
Water must be added to a low-maintenance battery
with removable cell caps before it is charged. Refer to
Battery Charging in the index of this service man-
ual for the location of the proper battery charging
procedures. A low electrolyte level may be caused by
an overcharging condition. Refer to Charging Sys-
tem in the index of this service manual for the loca-
tion of the proper charging system diagnosis and
testing procedures.

HYDROMETER TEST

The hydrometer test reveals the battery state-of-

charge by measuring the specific gravity of the elec-
trolyte.

This

test

cannot

performed

maintenance-free batteries with non-removable
cell caps. If the battery has non-removable cell caps,
refer to Built-In Test Indicator or Open-Circuit
Voltage Test in this section for the proper proce-
dures for performing these alternate tests of the bat-
tery state-of-charge.

Fig. 7 Built-In Test Indicator

1 – SIGHT GLASS
2 – BATTERY TOP
3 – GREEN BALL
4 – PLASTIC ROD

BATTERY

8A - 9

DIAGNOSIS AND TESTING (Continued)

Specific gravity is a comparison of the density of

the battery electrolyte to the density of pure water.
Pure water has a specific gravity of 1.000, and sulfu-
ric acid has a specific gravity of 1.835. Sulfuric acid
makes up approximately 35% of the battery electro-
lyte by weight, or 24% by volume. In a fully-charged
battery the electrolyte will have a temperature-cor-
rected specific gravity of 1.260 to 1.290. However, a
specific gravity of 1.235 or above is satisfactory for
battery load testing and/or return to service.

WARNING:

•

IF THE BATTERY SHOWS SIGNS OF FREEZ-

ING, LEAKING, LOOSE POSTS, OR LOW ELECTRO-
LYTE LEVEL, DO NOT TEST, ASSIST-BOOST, OR
CHARGE. THE BATTERY MAY ARC INTERNALLY
AND EXPLODE. PERSONAL INJURY AND/OR VEHI-
CLE DAMAGE MAY RESULT.

•

EXPLOSIVE HYDROGEN GAS FORMS IN AND

AROUND THE BATTERY. DO NOT SMOKE, USE
FLAME, OR CREATE SPARKS NEAR THE BATTERY.
PERSONAL INJURY AND/OR VEHICLE DAMAGE
MAY RESULT.

•

THE BATTERY CONTAINS SULFURIC ACID,

WHICH IS POISONOUS AND CAUSTIC. AVOID CON-
TACT WITH THE SKIN, EYES, OR CLOTHING. IN
THE EVENT OF CONTACT, FLUSH WITH WATER
AND CALL A PHYSICIAN IMMEDIATELY. KEEP OUT
OF THE REACH OF CHILDREN.

•

IF THE BATTERY IS EQUIPPED WITH REMOV-

Before testing, visually inspect the battery for any

damage (a cracked case or cover, loose posts, etc.)
that would cause the battery to be faulty. Then
remove the battery cell caps and check the electrolyte
level. Add distilled water if the electrolyte level is
below the top of the battery plates.

See the instructions provided by the manufacturer

of the hydrometer for recommendations on the cor-
rect use of the hydrometer that you are using.
Remove only enough electrolyte from the battery cell
so that the float is off the bottom of the hydrometer
barrel with pressure on the bulb released. To read
the hydrometer correctly, hold it with the top surface
of the electrolyte at eye level (Fig. 9).

CAUTION: Exercise care when inserting the tip of
the hydrometer into a battery cell to avoid damag-
ing the plate separators. Damaged plate separators
can cause early battery failure.

Hydrometer floats are generally calibrated to indi-

cate the specific gravity correctly only at 26.7° C (80°
F). When testing the specific gravity at any other
temperature, a correction factor is required. The cor-
rection factor is approximately a specific gravity
value of 0.004, which may also be identified as four
points of specific gravity. For each 5.5° C above 26.7°
C (10° F above 80° F), add four points. For each 5.5°
C below 26.7° C (10° F below 80° F), subtract four
points. Always correct the specific gravity for temper-
ature variation.

EXAMPLE: A battery is tested at -12.2° C (10° F)

and has a specific gravity of 1.240. Determine the
actual specific gravity as follows:

Fig. 8 Built-In Test Indicator Sight Glass

Fig. 9 Hydrometer - Typical

1 – BULB
2 – SURFACE COHESION
3 – SPECIFIC GRAVITY READING
4 – TEMPERATURE READING
5 – HYDROMETER BARREL
6 – FLOAT

8A - 10

BATTERY

DIAGNOSIS AND TESTING (Continued)

(1) Determine the number of degrees above or

below 26.7° C (80° F): 26.6° C - -12.2° C = 38.8° C
(80° F - 10° F = 70° F)

(2) Divide the result from Step 1 by 5.5° C (10° F):

38.8° C

4 5.5° C = 7 (70° F 4 10° F = 7)

(3) Multiply the result from Step 2 by the temper-

ature correction factor (0.004): 7 X 0.004 = 0.028

(4) The temperature at testing was below 26.7° C

(80° F); therefore, the temperature correction factor
is subtracted: 1.240 - 0.028 = 1.212

(5) The corrected specific gravity of the battery cell

in this example is 1.212.

Test the specific gravity of the electrolyte in each

battery cell. If the specific gravity of all cells is above
1.235, but the variation between cells is more than
fifty points (0.050), the battery should be replaced. If
the specific gravity of one or more cells is less than
1.235, charge the battery at a rate of approximately
five amperes. Continue charging the battery until
three consecutive specific gravity tests, taken at one-
hour intervals, are constant. If the cell specific grav-
ity variation is more than fifty points (0.050) at the
end of the charge period, replace the battery.

When the specific gravity of all cells is above 1.235,

and the cell variation is less than fifty points (0.050),
the battery may be load tested to determine its
cranking capacity. Refer to Load Test in this section
for the proper battery load testing procedures.

OPEN-CIRCUIT VOLTAGE TEST

A battery open-circuit voltage (no load) test will

show the state-of-charge of a battery. This test can be
used in place of the hydrometer test when a hydrom-
eter is not available, or for maintenance-free batter-
ies with non-removable cell caps.

WARNING:

•

IF THE BATTERY SHOWS SIGNS OF FREEZ-

ING, LEAKING, LOOSE POSTS, OR LOW ELECTRO-
LYTE LEVEL, DO NOT TEST, ASSIST-BOOST, OR
CHARGE. THE BATTERY MAY ARC INTERNALLY
AND EXPLODE. PERSONAL INJURY AND/OR VEHI-
CLE DAMAGE MAY RESULT.

•

EXPLOSIVE HYDROGEN GAS FORMS IN AND

AROUND THE BATTERY. DO NOT SMOKE, USE
FLAME, OR CREATE SPARKS NEAR THE BATTERY.
PERSONAL INJURY AND/OR VEHICLE DAMAGE
MAY RESULT.

•

THE BATTERY CONTAINS SULFURIC ACID,

WHICH IS POISONOUS AND CAUSTIC. AVOID CON-
TACT WITH THE SKIN, EYES, OR CLOTHING. IN
THE EVENT OF CONTACT, FLUSH WITH WATER
AND CALL A PHYSICIAN IMMEDIATELY. KEEP OUT
OF THE REACH OF CHILDREN.

•

IF THE BATTERY IS EQUIPPED WITH REMOV-

ABLE CELL CAPS, BE CERTAIN THAT EACH OF
THE CELL CAPS IS IN PLACE AND TIGHT BEFORE

THE BATTERY IS RETURNED TO SERVICE. PER-
SONAL INJURY AND/OR VEHICLE DAMAGE MAY
RESULT FROM LOOSE OR MISSING CELL CAPS.

Before proceeding with this test, completely charge

the battery. Refer to Battery Charging in the index
of this service manual for the location of the proper
battery charging procedures.

(1) Before measuring the open-circuit voltage, the

surface charge must be removed from the battery.
Turn on the headlamps for fifteen seconds, then
allow up to five minutes for the battery voltage to
stabilize.

(2) Disconnect and isolate both battery cables, neg-

ative cable first.

(3) Using a voltmeter connected to the battery

posts (see the instructions provided by the manufac-
turer of the voltmeter), measure the open-circuit volt-
age (Fig. 10).

See the Open-Circuit Voltage chart. This voltage

reading will indicate the battery state-of-charge, but
will not reveal its cranking capacity. If a battery has
an open-circuit voltage reading of 12.4 volts or
greater, it may be load tested to reveal its cranking
capacity. Refer to Load Test in this section for the
proper battery load testing procedures.

LOAD TEST

A battery load test will verify the battery cranking

capacity. The test is based on the Cold Cranking

Fig. 10 Testing Open-Circuit Voltage - Typical

Open Circuit Voltage

Open Circuit Volts

Charge Percentage

11.7 volts or less

12.0 volts

25%

12.2 volts

50%

12.4 volts

75%

12.6 volts or more

100%

BATTERY

8A - 11

DIAGNOSIS AND TESTING (Continued)

Content .. 79 80 81 82 ..