Testing; Hydrometer Test; Hydrometer - Jeep J-10 Series 1982 Technical & Service Manual

(4) When engine starts, remove jumper cables. Dis
connect cable from engine first.
(5) Discard cloth used to cover cap openings because
it has been exposed to sulfuric acid.
(6) Install battery caps.
TESTING
General
NOTE: A complete battery test includes cleaning the
top of the battery case, cleaning posts and cable termi
nals and performing hydrometer and heavy had tests.
The condition of a battery may be determined from
the results of two tests—state of charge (hydrometer
test) and ability to supply current (heavy load test).
Refer to Battery Diagnosis and Repair Simplification
(DARS) chart.
Perform the hydrometer test first. If specific gravity
indicates less than 1.225, the battery must be charged
before proceeding to further testing. A battery that will
not accept a charge is defective and further testing is not
necessary.
NOTE: A battery with sulfated plates may require an
overnight slow charge to determine if the sulfate coating
is thin enough to be eliminated by a charge.
A battery that is fully charged and does not pass the
heavy load test is defective.
If a battery discharges and no apparent cause can be
found, the battery should be fully charged and allowed
to stand on a shelf for three to seven days to determine if
the self-discharge is excessive. The Self-Discharge Rate
chart lists allowable self-discharge for the first ten days
of standing after a battery has been fully charged. A
battery is fully charged when all cells are gassing freely
and three corrected specific gravity tests, taken at one-
hour intervals, indicate no increase in specific gravity.
Hydrometer Test
NOTE: Periodically disassemble the hydrometer and
wash components with soap and water. Inspect the float
ft>r possible leaks. If the paper inside has turned brown,
the float is defective.
Prior to testing, visually inspect the battery for any
damage (cracked container, cover, loose post, etc.) that
would cause the battery to be unserviceable. To inter
pret the hydrometer correctly, hold it with the top sur
face of the electrolyte in the hydrometer at eye level (fig.
1D-2). Disregard the curvature of the liquid where the
surface rises against the float because of surface cohe
sion. Draw in only enough electrolyte to keep the float
off the bottom of the hydrometer barrel with the bulb
released. Keep the hydrometer in a vertical position
BATTERIES 1D-5
while drawing in the electrolyte and observing the spe
cific gravity. Exercise care when inserting the tip of the
hydrometer into a cell to avoid damage to separators.
Damaged separators can result in premature battery
failure.
BULB
THERMOMETER
DISREGARD
SLIGHT
CURVATURE
42143
Fig. 1D-2 Hydrometer
Hydrometer floats are generally calibrated to indicate
the specific gravity correctly at only one fixed temper
ature, 80°F (26.6°C). When testing the specific gravity
at any other temperature, a correction factor is re
quired. The correction factor is approximately a specific
gravity value of 0.004, referred to as 4 points of gravity.
For each 10°F above 80°F (5.5°C above 26.6°C), add 4
points. For each 10°F below 80°F (5.5°C below 26.6°C),
subtract 4 points. Alwayscorrect the specific gravity for
temperature variation. Test the specific gravity of the
electrolyte in each battery cell.
Example: A battery is tested at 10°F and has a spe
cific gravity of 1.240. The actual specificgravity is deter
mined as follows:
Number of degrees above or below 80°F equals 70
degrees (80 minus 10).
70° divided by 10° (each 10° difference) equals 7.
7 multiplied by 0.004 (temperature correction factor)
equals 0.028.
Temperature is below 80°F, therefore temperature
correction is subtracted.
Temperature corrected specific gravity is 1.212(1.240
minus 0.028).
A fully charged battery should have a temperature
corrected specific gravity of 1.250 to 1.265.
If the specific gravity of all cells is above1.235, but the
variation between cells is more than 50 points (0.050), it
is an indication that the battery is unserviceable. Re
move the battery from the vehicle for additional testing.
If the specific gravity of one or more cells is less than
1.235, recharge the battery at a rate of approximately 5