Dodge RAM TRUCK 1500 1995 Service Manual page 339

8A - 6 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICS
Exercise care when inserting the tip of the hydrom­
eter into a cell to avoid damaging the plate separa­
tors. Damaged plate separators can cause premature
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 correction factor is approximately a specific
gravity value of 0.004, referred to as 4 points of spe­
cific gravity. For each 5.5°C above 26.7°C (10°F above
80°F), add 4 points. For each 5.5°C below 26.7°C
(10°F below 80°F), subtract 4 points. Always correct
the specific gravity for temperature variation. Test
the specific gravity of the electrolyte in each battery
cell.
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 be­
low 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/10 = 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 is sub­
tracted:
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
variation between cells is more than 50 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 approxi­
mately 5 amperes. Continue charging until 3 consec­
utive specific gravity tests, taken at 1-hour intervals,
are constant. If the cell specific gravity variation is
more than 50 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 cell variation is less than 50 points (0.050), the
battery may be load tested.
OPEN CIRCUIT VOLTAGE TEST
A battery open circuit voltage (no load) test will
show state-of-charge of a battery. This test can be
used in place of the hydrometer test if a hydrometer
is not available, or for maintenance-free batteries
with non-removable cell caps.
Before proceeding with this test or load test,
completely charge battery as described in Bat­
tery Charging in this group.
Test battery open circuit voltage as follows:
(1) Before measuring open circuit voltage the sur­
face charge must be removed from the battery. Turn
headlamps on for 15 seconds, then allow up to 5 min­
utes for voltage to stabilize.
(2) Remove both battery cables, negative first. On
diesel engine models with dual batteries, each bat­
tery must be disconnected and tested separately from
the other.
(3) Using a voltmeter connected to the battery
posts (refer to instructions provided with voltmeter)
measure open circuit voltage (Fig. 5).
See Open Circuit Voltage chart. This voltage read­
ing will indicate state-of-charge, but will not reveal
cranking capacity. If a battery has an open circuit
voltage reading of 12.4 volts or greater, it may be
load tested. A battery that will not endure a load test
is faulty and must be replaced.
OPEN CIRCUIT VOLTAGE
Open Circuit ¥©its
11.7 volts or less 0%
12.0
25%
12.2 50%
12.4
75%
12.6 or more 100%
928A-3
898A-7
Fig. 5 Testing Open Circuit Voltage
LOAD TEST
A battery load test will verify battery cranking ca­
pacity. The test is based on the Cold Cranking Am­
perage (CCA) rating of the battery. See Battery
Classifications and Ratings chart in Specifications, at
the back of this group.
WARNING; IF BATTERY S H O W S S I G N S OF F R E E Z ­
ING, LEAKING, L O O S E P O S T S , OR L O W E L E C T R O ­
LYTE L E V E L , DO NOT LOAD TEST. P E R S O N A L
INJURY AND/OR VEHICLE DAMAGE MAY RESULT.