GMC 1976 ZEO 6083 Maintenance Manual page 389

* If specific gravity readings show a difference
between the highest and lowest cell of .050 (50
points) or more, the Battery is defective and should
be replaced .
Since the battery is a perishable item which re-
quires periodic servicing, a good maintenance pro-
gram will insure the longest possible Battery life . If
the battery tests good but fails to perform satisfac-
torily in service for no apparent reason, the following
are some of the more important factors that may
point to the cause of the trouble .
1 . Vehicle accessories inadvertently left on over-
night to cause a discharge condition.
2. Slow speed driving of short duration, to cause
an undercharged condition .
3. A vehicle electrical load exceeding the genera-
tor capacity .
4 . Defect in the charging system such as high
resistance, slipping fan belt, faulty generator or volt-
age regulator.
5. Battery abuse, including failure to keep the
Battery top clean, cable attaching bolts clean and
tight, and improper addition of water to the cells.
TESTING MAINTENANCE-FREE
BATTERIES
Step 1-Visual Inspection
Check for obvious damage, such as cracked or
broken case or cover that could permit loss of elec-
trolyte . If obvious physical damage is noted, replace
battery. Determine cause of damage and correct as
needed .
Step 2-Charge Indicator
Check the charge indicator. For a detailed dis-
cussion on how to read the charge indicator, refer to
"Charging Guide" later in this section.
a. Green dot visible. If the charge indicator is
dark and has a green dot in the center, the battery
is sufficiently charged for testing. Proceed to Step 3.
b. Dark green dot not visible. Battery must be
charged before testing . Refer to "Chargine Guide"
later in this section. Once battery is charged, proceed
to Step 3.
NOTE : Battery should be charged until green dot
appears, but not more than 60 ampere hours (for
example-15 amperes for four hours) . Some
ENGINE ELECTRICAL
6Y- 9
chargers are constant current chargers, but if a
constant voltage charger is used, to get the green
dot to appear after prolonged charging may re-
quire tipping the battery slightly from side to
side a few times.
c. Light . DO NOT attempt charging or test-
ing when charge indicator is light . Refer to "Charg-
ing Guide" later in this section.
CAUTION:
To avoid explosion hazard,
NEVER attempt to charge or jump-start a
maintenance-free battery which exhibits a
light indicator condition. Departures from
this procedure could result in serious per-
sonal injury or property damage.
Step 3-Remove Surface Charge
Connect 300 ampere load across terminals for 15
seconds to remove surface charge from battery.
Step 4-Load Test
a. Connect voltmeter and 230 ampere load
across terminals.
b. Read voltage after 15 seconds with load
connected, then disconnect load .
c. If minimum voltage agrees with Chart
(given in Specifications) battery is good .
d. If minimum voltage is less than given in
Chart replace battery.
INSTALLING BATTERIES
To install a battery properly, it is important to
observe the following precautions:
*Connect grounded terminal of Battery last to
avoid short circuits which may damage the electrical
system .
Do not connect primary lead until secondary
negative cable wire has been grounded to sheet
metal .
* Be sure there are no foreign objects in the car-
rier, so that the new Battery will rest properly in the
bottom of the carrier.
* Tighten the hold-down evenly until snug (5-6
ft . lbs.) . Do not draw down tight enough to distort
or crack the case or cover.
e Be sure the cables are in good condition and the
terminal bolts are clean and tight. Make sure the