GMC 4000 Series Service Manual page 404

Good Battery (Fig. 2, View A)
If all cells read 1.95 volts or more and the
difference between the highest and lowest cell is
le s s than .05 volt, battery is good.
Good Battery (Fig. 2, View B)
If cells read both above and below 1.95 volts
and the difference between the highest and lowest
cell is le ss than .05 volt, battery is good but re­
quires charging. See "Charging After Light Load
T est."
Replace Battery (Fig. 2, View C)
If any cell reads 1.95 volts or more and there
is a difference of .05 volts or more between the
highest and lowest cell, the battery should be re­
placed.
Discharged Battery (Fig. 2, View D)
If all cells read le ss than 1.95 volts, battery
is too low to test properly. FAILURE OF THE
METER TO REGISTER ON ALL CELLS DOES
NOT INDICATE A DEFECTIVE BATTERY. Boost
charge battery and repeat "Light Load T est." (See
"Boost Charging For Light Load Test.") If battery
is found to be good after boosting, it should be fully
recharged for good performance. If none of the
cells come up to 1.95 volts after the first boost
charge, the battery should be given a second boost.
B atteries which do not respond after a second boost
charge should be replaced.
NOTE: If any battery found to be good by the
"Light Load Test" does not perform satisfactorily
in subsequent service, it should again be tested by
the "Light Load Test" and if it still tests "good"
it should be removed from vehicle and tested as
outlined under "Full Charge Hydrometer Test."
BOOST CHARGING FOR THE LIGHT LOAD TEST
Boost charge 12-volt batteries having an am­
pere hour capacity of 100 or le s s at 50 amperes
for 20 minutes (50 x 20 = 1000 ampere minutes).
Boost charge batteries having an ampere hour ca­
pacity of over 100 at 60 amperes for 30 minutes
(60 x 30 = 1800 ampere hour minutes). If charger
will not give this rate, charge for an equal number
of ampere minutes at best rate available.
IMPORTANT: For purposes of this test, do
not boost battery more than the amount indicated.
CHARGING AFTER THE LIGHT LOAD TEST
For best performance, a good battery should
be fully charged before being returned to service.
If batteries are to be fully charged by means
of a quick charger, the charge rate must be "taper­
ed" (reduced to a safe limit) when the electrolyte
temperature reaches 125°F., or when gassing be­
com es excessive. Failure to do so may harm the
battery.
G M C S E R V I C E M A N U A L
FULL CHARGE HYDROMETER TEST
not only with the percentage of acid in the liquid,
but also with temperature. As temperature in­
creases, the electrolyte expands so that the specific
gravity is reduced. As temperature drops, the
electrolyte contracts and specific gravity increas­
es. Unless these variations are noted, the specific
rates. Refer to applicable chart.
CHART 1:
CHART 2:
CHART 3:
Amp-Hour
Capacity
The specific gravity of the electrolyte varies
CHARGING GUIDE FOR BATTERIES
Below is a suggested list of battery charging
For dry charged batteries being ac­
tivated with electrolyte at a temper­
ature under 60°F., or with batteries
which are expected to go into immed­
iate operation in below freezing wea­
ther.
Amp-Hour Dry Battery
Warm-up Charge
Capacity
100
or
Less
Over
100
For batteries which require a boost
charge for the "Light Load Test"
procedures.
Amp-Hour Light Load Test
Capacity Boost Charge
100
or
Less
Over
100
For batteries which have become
discharged and require charging. It
should be recognized that slow charg­
ing is the best and only method of
completely recharging batteries. How­
ever, since time is often of import­
ance, two other methods are offered
for partial battery re-charges listed
in this chart.
Slow / Fast
Charging Charging
24 Hours 1-1/2 Hrs. 30 Minutes
100
or
4 Amps 40 to
Less
50 Amps
24 Hours 3 Hours
Over
9 Amps 40 to
100
50 Amos
Sec. 6Y
Page 393
BATTERY
10 Min.
15 Amps
10 Min.
30 Amps
________
20 Min.
50 Amps
30 Min.
60 Amps
Emergency
Boost Charging
40 to 50 Amps
1-1/2 Hours
40 to 50 Amps