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BATTERIES
BATTERY TESTING – 12 VOLT
See General Warnings on page 1-1.
Four tests have been developed to help diagnose problems with batteries that have not performed as expected.
Because each test becomes progressively more detailed and time-consuming, begin with the first test and follow
through with the other tests until the problem has been identified as outlined in the Battery Troubleshooting Chart
(Figure 16-1, Page 16-2).
BATTERY CHARGER TEST
The easiest way to monitor the condition of a vehicle's batteries is simply to observe the reading on the battery charger
ammeter at the end of the charge cycle. After a full charge, disconnect the charger DC plug, wait 20 to 30 seconds and
reconnect the charger DC plug. The ammeter needle will jump to 15 amps or more and then taper to below 6 amps
within 10 to 20 minutes, indicating sound, fully charged batteries.
Continued poor performance may indicate a problem in the vehicle electrical system, brakes or battery charger. If the
problem is not found in the vehicle or charging system, proceed to the on-charge voltage test. Batteries that remain at
8 amps or higher should be tested further using the on-charge voltage test.
ON-CHARGE VOLTAGE TEST
When the batteries are fully charged, disconnect the charger DC plug. Wait 20 to 30 seconds and reconnect the DC
plug to restart the charger. After 5 minutes, use a multimeter to check and record the voltage of the battery set as
well as the individual batteries. Set the multimeter to 200 volts DC. Place the red (+) probe on the positive (+) post of
battery no. 1 and the black (–) probe on the negative (–) post of battery no. 4 (Figure 16-6, Page 16-16). Record
reading. Then set multimeter to 20 volts DC and place the red (+) probe on the positive (+) post and the black (–) probe
at the negative (–) post of each battery. Record the readings.
The on-charge voltage for the set should be between 56.0 volts and 63.0 volts depending on the age and state of
charge of the batteries being tested. If individual batteries read above 14.0 volts and are within 1.0 volts of each other,
go to the hydrometer test. If any battery reads below 14.0 volts and not within 1.0 volts of those batteries above
14.0 volts, replace battery. If readings are below 14.0 volts but within 1.0 volts of each other, the batteries are old.
Old batteries may have enough capacity left to last several more months. Go to hydrometer test. See Battery
Troubleshooting Chart on page 16-2 and the examples on the following pages.
HYDROMETER TEST
A hydrometer measures the specific gravity of the battery's electrolyte. The higher the specific gravity, the higher the
state of charge of the batteries. A fully charged battery should read between 1.250 and 1.280 at 80 °F (26.7 °C). Never
add acid to batteries to obtain a higher specific gravity.
Performing the Hydrometer Test
1.
Be sure batteries have sufficient electrolyte to cover plates by approximately 1/2 inch (13 mm) and are fully
charged prior to beginning test. If water must be added, recharge the batteries before performing the hydrometer
test. See following CAUTION.
2008 Electric Precedent Maintenance and Service Manual
Battery Testing – 12 Volt
Page 16-3
16
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Troubleshooting
