TRUCK SERVICE MANUAL
The Slow Charge method uses a low charging rate for a
relatively long period of time. The recommended rate for slow
charging is one ampere per positive plate per cell. If the
battery has nine plates per cell, normally four of the nine will
be positive plates. Therefore, the slow charge rate would be
four amperes. Charging periods as long as twenty-four hours
may be needed to bring a battery to full charge.
The best method of making certain a battery is fully charged,
but not overcharged is to measure the specific gravity of a cell
once per hour. The battery is fully charged when no change
in specific gravity occurs over a three hour period or when
charging current stabilizes (constant voltage type charger).
If a low maintenance (conventional) battery is to be charged
overnight (10-16 hours) use the specified Slow Charge rate
Maintenance free batteries must not be charged at rates
greater than specified in the Maintenance-Free Battery
Charging Guide (Table 7).
If a maintenance free battery is to be recharged overnight, (16
hours) a timer or voltage controlled charger is recommended.
If the charger does not have such controls, a 3 ampere rate
should be used for batteries of 80 minutes or less capacity
and 5 amperes for above 80 to 125 minutes reserve capacity
batteries. Batteries over 125 minutes should be charged at
the specified Slow Charge rate (Table 7).
Batteries that have stood in a discharged condition for long
periods of time without a recharge, have become sulfated and
must be recharged at a low rate to avoid overheating and
excessive gassing. It may require two or three days of slow
charging to bring a sulfated battery to a fully charged
condition. Care should be taken not to overcharge
maintenance free type batteries.
Some batteries are so badly sulfated they can not be restored
to a normal operating condition, regardless of the rate of
charge or the length of time the charge is applied. Therefore,
if a battery cannot be restored to a fully charged condition by
slow charging, it should be rejected.
The Fast Charge method provides a high charging rate for a
short period of time. The charging rate should be limited to
60 amperes for 12-volt batteries. Maximum charging rate for
6-volt batteries (above 180 reserve capacity minutes) can be
approximately double this value.
Ideally, fast charges should be limited to the charging times
shown under Fast Charge in the Battery Charging Guides,
Tables 6 and 7. The battery generally cannot be fully charged
within these time periods; but it will receive sufficient charge
(70 to 90%) for practical service. To completely recharge a
battery, follow the fast charge with a slow charge until no
change in specific gravity occurs over a three hour period.
A battery with electrolyte specific gravity of 1.225 or above,
should never be charged at a high rate. If the charger has not
tapered to a low rate, adjust to a slow charge, preferably at a
rate of one ampere per positive plate per cell.
Before placing a battery on charge, clean the battery terminals
if necessary. Add water sufficient to cover the plates. Fill to
the proper level near the end of charge. If the battery is
extremely cold, allow it to warm before adding water because
the level will rise as it warms. In fact, an extremely cold
battery will not accept a normal charge until it becomes warm.
Following instructions of charger manufacturer, connect
charger to battery.
Connect the positive (+) charger lead to positive battery
terminal and negative (-) lead to negative terminal. If the
battery is in the vehicle, connect the negative lead to the
engine block if the vehicle has a "negative ground" (negative
battery terminals is connected to ground). Connect the
positive lead to ground if vehicle has a "positive ground".
"Rock" the charger lead clamps to make certain a good
connection has been made.
Turn the charger "ON" and slowly increase the charging rate
until recommended ampere value is reached.
CTS-2771 Page 15
PRINTED IN UNITED STATES OF AMERICA