Pontiac FIREBIRD 1972 Service Manual page 1295

CHASSIS ELECTRICAL 12-25
Interpretation
Specific Gravity
Difference Between
Highest and
Lowest Cells
Less than 50 points
Less than 50 points
More than 50 points
Specific Gravity
of Lowest Cell
(Temp. Corrected)
More than 1.200
Less than 1.200
Good Battery
-
Satisfactorily Charged
Good Battery
-
Requires Charging
Defective Battery
-
Replace
Fig. 1 2 - 2 6 Specific Gravity Chart
mine the condition of any 12-volt unit. The conditions,
good, defective or amount of battery charge can quickly
be determined. The tester can be used with the battery
either in or out of the vehicle, regardless of size or temper-
ature. Terminal adapters are readily available for side ter-
minal battery hook-up (Fig. 12-28).
The 421 tester is based on an analysis of the difference
between two voltage readings. One of these voltage read-
ings is taken after the battery has been discharged at a
given rate and time by the tester. The other reading is
taken after the battery has be'en charged at a given rate and
time by the tester. The difference between these two read-
ings is then compared with a standard shown on the tester.
The conditions of good or defective and the state-of-
charge can quickly be determined.
421 testers which automatically charge and discharge the
test battery at a given rate and time are manufactured and
sold by a number of companies. The 421 designation is
shown on the meter face indicating that the above de-
scribed programmed test is followed. For particulars in
the use of the test, follow the specific directions of the test
equipment manufacturer.
If a 421 tester is not available for the solid-top batteries,
a hydrometer and thermometer may be used as a prelimi-
nary check for this type battery. The accuracy of this
Fig. 12-27 4 2 1 Battery Tester
check, described below, is not sufficient to be considered
as a reliable battery test. All batteries passing the hydrom-
eter check, would not necessarily pass the 421 test nor
perform its normal function. General comments on ove-
rall 421 Tester operation follow:
Energizers or batteries should NOT be charged prior to
making this test. Defects within the unit can be hidden by
the charging and erroneous test results will be obtained.
Erratic or extremely low initial meter readings may indi-
cate poor connections at the tester terminals. Obtain clean
and tight connections before performing the 42 1 test.
All meter readings should be made immediately after the
meter indicator light comes on even if the meter needle is
still moving.
If additional discharges are required after the initial dis-
charge, set meter indicator following the last discharge
cycle.
Batteries designated as bad by the tester should be re-
placed.
Batteries designated as good, with no owner's complaint
L
Fig. 1 2 - 2 8 Side Terminal Battery Adapters