16
Battery Testing – 12 Volt
BATTERIES
BATTERY TROUBLESHOOTING EXAMPLES
The following information represents a few examples of troubleshooting battery problems.
Example 1
Vehicle no. 68 was suspected of having a bad battery due to its performance. As a result, the battery charger test
was performed. After a full charge, the battery charger ammeter read 8.0 amps. Next, the on-charge voltage test
was performed and the following results were recorded:
BATTERY NO.
1
2
3
4
On-Charge Voltage
15.22 V
15.90 V
14.70* V
15.24 V
*Battery no. 3 appears suspect. Battery nos. 1 and 4 are also suspect. Next, a hydrometer test should be conducted
on all batteries.
Hydrometer test results:
BATTERY NUMBER
CELL NUMBER
1
2
3
4
Cell 1 (Positive Post)
1.200*
1.265
1.300
1.250
Cell 2
1.285
1.275
1.290
1.270
Cell 3
1.265
1.270
1.275
1.265
Cell 4 (Negative Post)
1.275
1.270
1.285
1.265
Cell 5
1.270
1.265
1.280
1.270
Cell6
1.275
1.280
1.280
1.260
*After the hydrometer test, it appears that battery no. 1 is the problem. Next, the discharge test was performed.
Discharge test results:
BATTERY NO.
1
2
3
4
Discharge Voltage
8.16* V
10.99 V
11.60 V
10.72 V
*After a discharge test which lasted 45 minutes, battery no. 1 is clearly shown to be the problem. Battery no. 4 should
be watched a little more closely but appears to be okay. Battery no. 1 should be replaced with a battery that has about
the same age and usage as the other batteries in the set.
Example 2
Vehicle no. 70 was also suspected of having a bad battery due to its performance. The battery charger test showed
7.0 amps after a full charge. After confirming there were no problems with the electrical system, charger or brakes, the
on-charge voltage was recorded as follows:
BATTERY NO.
1
2
3
4
On-Charge Voltage
15.72 V
14.66* V
15.80 V
15.85 V
*Battery no. 2 was immediately suspected as the problem. After checking battery no. 2 with a hydrometer, it was
discovered that the negative post cell was completely dead. Battery no. 2 should be replaced with a battery that has
the same age and usage as the other batteries in the set.
Page 16-8
2009 Electric Precedent Maintenance and Service Manual