Jeep 1997 Grand Cherokee Service Manual page 308

8A - 8 BATTERY
DIAGNOSIS AND TESTING (Continued)
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:
(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 (10):
38.8° C 5.5 = 7 (70° F
(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
The corrected specific gravity of the battery in this
example is 1.212.
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 consecu-
tive specific gravity tests, taken at one-hour inter-
vals, are constant. If the cell specific gravity
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. See the Load Test procedure in
this group for more information.
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.
10 = 7)
Before proceeding with this test, completely charge
the battery as described in the Battery Charging pro-
cedure in this group.
(1) Before measuring the open-circuit voltage, the
surface charge must be removed from the battery.
Turn on the head lamps 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 (refer to the instructions provided with the
voltmeter), measure the open-circuit voltage (Fig. 5).
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. See the Load Test procedure in this group
for more information.
Fig. 5 Testing Open-Circuit Voltage - Typical
Open Circuit Voltage
Open Circuit Volts
11.7 volts or less
12.0 volts
12.2 volts
12.4 volts
12.6 volts or more
ZG
Charge Percentage
0%
25%
50%
75%
100%