GMC 4000 Series Service Manual page 405

Sec. 6Y
Page 394
BATTERY
gravity obtained by the hydrometer may not give a
true indication of the concentration of acid in the
electrolyte.
Corrections can be made for temperature by
adding .004 (four points of gravity) to the hydrom­
eter reading for every 10°F., that the electrolyte
is above 80°F., or by subtracting .004 for every
10°F., that electrolyte is below 80°F.
1. Adjust electrolyte to proper level in each
cell by adding water, then replace vent caps.
2. Charge the battery in accordance-with ap­
plicable chart under "Charging Guide For Batter­
ies."
3. Using a hydrometer, measure specific grav­
ity of electrolyte in each cell. If any cell reads
le ss than 1.230 (corrected to 80°F.) the battery
should be replaced.
CAUTION: DO NOT take hydrometer
readings immediately after water has
been added. Water must be thoroughly
mixed with electrolyte by charging for at
least 15 minutes at a rate high enough to
cause vigorous gassing.
4. If any cell reads above 1.310, the battery
may be returned to service. However, specific
gravities above 1.310 are harmful to the battery.
BATTERY CHARGING
When a battery is being charged, an explosive
gas mixture forms in each cell. Part of this gas
escapes through holes in the vent plugs and may
form an explosive atmosphere around the battery
if ventilation is poor. This gas may remain in or
around the battery for several hours after it has
been charged. Sparks or flames can ignite this gas
causing an internal explosion which may shatter
the battery; therefore, do not smoke near a battery
which is being charged or which has been recently
charged and exercise care when connecting or dis­
connecting booster leads or cable clamps on a
charger. Poor connections are a common cause of
electrical arcs which cause explosions.
There are three methods of recharging bat­
teries. They differ basically in the length of time
the battery is charged and the rate at which charg­
ing current is supplied. One is the "Slow Charge"
method, the second is the "Fast Charge" method,
and the third is the "Emergency Boost Charge"
method.
Before recharging a battery by any method,
the electrolyte level must be checked and adjust­
ed, if necessary.
SLOW CHARGING
The "Slow Charge" method supplies the battery
with a relatively low current flow for a relatively
G M C S E R V I C E M A N U A L
long period of time. This is the only method that
will bring the battery to a full state of charge.
at approximately a 4-ampere rate for 24 hours or
more, if necessary, to bring the battery to full
charge. A fully charged condition is reached when
the cells are gassing freely and three corrected
specific gravity readings taken at hourly intervals
show no increase.
FAST CHARGING
the battery at a 40 to 50 ampere rate for a 1 -1 /2 -
hour period of time. If the electrolyte temperature
reaches 125°F., before the 1-1/2-hour period is
completed, the battery must be taken off charge
temporarily, or the charging rate reduced to avoid
damage to the battery.
charged condition during "Fast Charge," it can be
substantially recharged or "boosted." In order to
bring the battery to a fully charged condition, the
charging cycle must be finished by the "Slow
Charge" method.
EMERGENCY BOOST CHARGING
charged to crank the engine, an emergency boost
charge may be applied as a temporary expedient
in order to crank the engine. The "Emergency
Boost Charge" method consists of charging at a 40
to 50 ampere rate for a period of one-half hour.
gency Boost Charge" will not necessarily restore
the battery to a useful state of charge for continued
service. After an "Emergency Boost Charge" fail­
ure to charge the battery further, either by a long
uninterrupted driving period or by the "Fast
Charge" or "Slow Charge" method, may result in
failure to crank the engine the next time cranking
is attempted. A battery should never be condemned
on the basis of failure to crank the engine after an
"Emergency Boost Charge." Although an emergency
boost charge may put enough energy into the bat­
tery to crank the engine once, further charging
usually is necessary in order to create a sufficient
reserve to crank a second and third time.
NEW VEHICLES IN STOCK
ceived; add sufficient distilled water to bring the
electrolyte up to bottom of vent w ells. DO NOT
OVERFILL.
as necessary at weekly or semi-monthly intervals,
depending upon the weather. Warm weather causes
greater water lo ss.
low 1.215 (corrected to 80°F.), remove it from
The "Slow Charge" method consists of charging
The "Fast Charge" method supplies current to
Although a battery cannot be brought to a fully
In cases where the battery is not sufficiently
It should be particularly noted that the "Emer­
1. Check electrolyte on each new vehicle re­
2. Check electrolyte and add distilled water
3. If the specific gravity of the battery is be­