GMC 4000 Series Service Manual page 402

3. When attaching battery charger leads to the
battery, connect charger positive lead to battery
positive terminal and connect charger negative
lead to battery negative terminal.
4. DO NOT smoke near a battery which is be­
ing charged.
COMMON CAUSES OF BATTERY FAILURE
When a battery fails, the cause of failure may
lie outside the battery itself. For this reason, when
a battery failure is encountered, do not be satis­
fied to merely recharge or replace it. Find the
cause of the failure and prevent recurrence of the
trouble. Listed below are some of the common
causes of battery failure:
1. Defect in generating system such as high
resistance, slipping generator drive belt, faulty
generator or regulator.
2. Overloads caused by defective starter or
excessive use of a ccessories.
3. Battery abuse, including failure to keep
battery top clean, cable clamps clean and tight,
and improper addition of water to the cells.
4. Hardened battery plates, commonly called
"sulfation," due to battery being in a low state of
charge over a long period of time.
5. Physical defects such as shorted cells, loss
of active material from plates, etc.
6. Driving conditions or requirements under
which the vehicle is used only for short drives.
BATTERY TESTS
Testing procedures are used to determine
whether the battery is: (1) Good andusable, (2) Re­
quires recharging, or (3) Should be replaced.
The following checks may be performed to
determine condition of the battery.
VISUAL INSPECTION
The first step in testing the battery should be
a visual inspection, which very often will save time
and expense in determining battery condition.
1. Check outside of battery for a broken or
cracked case or a broken or cracked cover. If
damage is evident, the battery should be replaced.
2. Check the electrolyte level. Levels that are
too high or too low will cause poor performance.
3. Check for loose terminal posts, cable con­
nections, and for evidence of corrosion. Correct
as required before proceeding with tests.
CAPACITY TEST
This test is one means of determining whether
a battery is functioning efficiently to the degree
where it can be relied upon to perform all of its
duties properly in the vehicle.
A 6-volt battery that will maintain 4.5 volts
and a 12-volt battery that will maintain 9.0 volts
G M C S E R V I C E M A N U A L
LO A D (VARIABLE
RESISTANCE)
O
AMMETER
or better during a capacity test should be consid­
ered a good battery. To make this test, use equip­
ment that will take a heavy electrical load from
the battery such as a carbon pile or other suitable
means. If test equipment is not available for load­
ing battery the starter may be used as a load.
leads to battery positive post and negative volt­
meter and ammeter leads to battery negative post
(fig. 2).
battery posts; voltmeter cable clips must contact
battery post or cable clamp.
the ampere-hour rating of the battery for 15 s e c ­
onds. Refer to "Specifications" at end of this se c ­
tion for ampere-hour ratings of various batteries
used in vehicles covered by this manual.
voltage which should not be le ss than 4.5 volts for
6-volt battery or 9.0 volts for 12-volt battery.
tery or 9.0 volts for 12-volt battery or more, bat­
tery has good output capacity and will readily
accept a normal charge.
4.5 volts for a 6-volt battery or 9.0 volts for a 12-
volt battery, perform the "Battery Instrument
Test" or "Battery Light Load T est."
oooooo
o o rA
C fc
Figure 2 — Battery Capacity Test
1. Connect positive voltmeter and ammeter
NOTE: Ammeter cable clips must contact
2. Apply a load to the battery of three tim es
3. With ammeter reading specified load, read
a. If voltmeter shows 4.5 volts for 6-volt bat­
(1) If specific gravity is 1.215 or more, no
service is required.
(2) If specific gravity is below 1.215, check
charging circuit to determine the cause
and correct as required. The battery should
be slow-charged for city driving. With high­
way driving and a good charging system ,
the battery should charge satisfactorily.
b. If voltmeter shows a reading of le s s than
Sec. 6Y
Page 391
BATTERY
ll>
VOLTMETER
TPM-4251