(2) Disconnect and isolate the battery negative
cable. Connect the battery charger leads. Some bat-
tery chargers are equipped with polarity-sensing cir-
cuitry. This circuitry protects the battery charger and
the battery from being damaged if they are improp-
erly connected. If the battery state-of-charge is too
low for the polarity-sensing circuitry to detect, the
battery charger will not operate. This makes it
appear that the battery will not accept charging cur-
rent. See the instructions provided by the manufac-
turer of the battery charger for details on how to
bypass the polarity-sensing circuitry.
(3) Battery chargers vary in the amount of voltage
and current they provide. The amount of time
required for a battery to accept measurable charging
current at various voltages is shown in the Charge
Rate Table. If the charging current is still not mea-
surable at the end of the charging time, the battery
is faulty and must be replaced. If the charging cur-
rent is measurable during the charging time, the bat-
tery may be good and the charging should be
completed in the normal manner.
CHARGE RATE TABLE
Voltage
Hours
16.0 volts maximum
up to 4 hours
14.0 to 15.9 volts
up to 8 hours
13.9 volts or less
up to 16 hours
CHARGING TIME REQUIRED
The time required to charge a battery will vary,
depending upon the following factors:
• Battery Capacity - A completely discharged
heavy-duty battery requires twice the charging time
of a small capacity battery.
• Temperature - A longer time will be needed to
charge a battery at -18° C (0° F) than at 27° C (80°
F). When a fast battery charger is connected to a cold
battery, the current accepted by the battery will be
very low at first. As the battery warms, it will accept
a higher charging current rate (amperage).
• Charger Capacity - A battery charger that
supplies only five amperes will require a longer
charging time. A battery charger that supplies
twenty amperes or more will require a shorter charg-
ing time.
• State-Of-Charge - A completely discharged bat-
tery requires more charging time than a partially
discharged battery. Electrolyte is nearly pure water
in a completely discharged battery. At first, the
charging current (amperage) will be low. As the bat-
tery charges, the specific gravity of the electrolyte
will gradually rise.
The Battery Charging Time Table gives an indica-
tion of the time required to charge a typical battery
at room temperature based upon the battery state-of-
charge and the charger capacity.
BATTERY CHARGING TIME TABLE
Charging Amper-
age
5 Amps
10
Amps
20 Amps
Open Circuit Volt-
age
Hours Charging @ 21° C (70°
F)
12.25 to 12.49
6 hours
3 hours
1.5
hours
12.00 to 12.24
10 hours
5 hours
2.5
hours
10.00 to 11.99
14 hours
7 hours
3.5
hours
Below 10.00
18 hours
9 hours
4.5
hours
STANDARD PROCEDURE - OPEN - CIRCUIT
VOLTAGE TEST
A battery open-circuit voltage (no load) test will
show the approximate state-of-charge of a battery.
This test can be used in place of the hydrometer test
when a hydrometer is not available, or for mainte-
nance-free batteries with non-removable cell caps.
Before proceeding with this test, completely charge
the battery (Refer to 8 - ELECTRICAL/BATTERY
SYSTEM/BATTERY - STANDARD PROCEDURE).
(1) Before measuring the open-circuit voltage, the
surface charge must be removed from the battery.
Turn on the headlamps for fifteen seconds, then
allow up to five minutes for the battery voltage to
stabilize.
(2) Disconnect and isolate both battery cables, neg-
ative cable first.
Fig. 4 VOLTMETER ACCURATE TO 1/10 VOLT
VA
BATTERY SYSTEM
8F - 9