GMC 4000 Series Service Manual page 403

Sec. 6Y
Page 392
BATTERY
All cells read 1.95 or higher
L es s t h a n . 0 5 v ol t
GOOD BATTERY
© One or more cells read 1.95 or higher
REPLACE BATTERY
BATTERY INSTRUMENT TEST
NOTE: A number of suppliers have approved
testing equipment available, such as the tester (J-
22552).
These testers have a programmed test pro­
cedure consisting of a series of timed discharge
and charge cycles that will determine the condition
of the battery with a high degree of accuracy. When
using these testers, follow procedures recom­
mended by the instrument manufacturer.
If a tester is not available, the "Specific Grav­
ity Cell Comparison Test" may be used as an al­
ternate method, but with a sacrifice in testing
accuracy.
1. Measure specific gravity of each cell, re­
gardless of state of charge.
2. If specific gravity readings show a differ­
ence between the highest and lowest cell of 0.050
(50 points) or more, the battery should be replaced.
G M C S E R V I C E M A N U A L
Sufficiently Charged
Figure 3 — Battery Light Load Test
( j * ) Cells read both above and below 1.95
GOOD BATTERY
All cells read less than 1.95
BOOST-CHARGE AND RETEST
BATTERY LIGHT-LOAD TEST
CAUTION: DO NOT attempt to per­
form this test on batteries which have a
one-piece cell cover (fig. 1).
Check electrical condition of battery cells as
follows (refer to fig. 3):
1. If electrolyte level in each cell is low, ad­
just to proper level by adding colorless, odorless,
drinking water.
2. Place load on battery by cranking engine.
If engine starts, turn off ignition immediately. If
engine does not start, hold starter switch "ON"
for 3 seconds, then release.
3. Turn on head lights (low beam). After one
minute, with lights still "ON" read voltage of each
battery cell with voltmeter, compare readings with
the following:
Requires Charging
T -5 0 8 -1