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Battery Inspection
Common Causes of Failure
A battery is not designed to last indefinitely; however, with proper care, it will provide many years of service. If the battery performs satisfactorily during test but fails to operate properly for no apparent reason, the following are some factors that may point to the cause of trouble:
• Accessories left on overnight or for an extended period without the generator operating.
• Slow average driving speeds for short periods.
• Electrical load exceeding generator output particularly with addition of aftermarket equipment.
• Defects in charging system such as high resistance, slipping drive belt, loose generator output terminal, faulty generator of voltage regulator. Refer to Generator Symptom Diagnosis:M13A .
• Battery abuse, including failure to keep battery cable terminals clean and tight or loose battery hold down.
• Mechanical problems in electrical system such as shorted or pinched wires.
Visual Inspection
Check for obvious damage, such as cracked or broken case or cover, that could permit loss of electrolyte. If obvious damage is noted, replace battery. Determine cause of damage and correct as needed.
Hydrometer Test
The direct method of checking the battery for state of charge is to carry out a high rate discharge test, which involves a special precise voltmeter and an expensive instrument used in the service shops, but not recommendable to the user of the vehicle.
At 20 °C of battery temperature (electrolyte temperature):
• The battery is in FULLY CHARGED STATE if the electrolyte S.G. is 1.280.
• The battery is in HALF CHARGED STATE if the S.G. is 1.220.
• The battery is in NEARLY DISCHARGED STATE if the S.G. is 1.150 and is in danger of freezing.
As the S.G. varies with the temperature, if battery temperature is not at 20 °C (68 °F), you have to correct your S.G. reading (taken with your hydrometer) to the value at 20 °C (68 °F) and apply the corrected S.G. value to the three-point guide stated value.
For the manner of correction, refer to the graph showing the relation between S.G. value and temperature.
How to use the temperature-corrected state-of-charge graph
Suppose your S.G. reading is 1.28 and the battery temperature is –5 °C (23 °F). Locate the intersection of the –5 °C line and the 1.28 S.G. line.
The intersection is within the “A” zone (shaded area in the graph) and that means CHARGED STATE.
To know how much the battery is charged, draw a line parallel to the zone demarcation line and extend it to the right till it meets with the percentage scale. In the present example, the line meets at about 85% point on the percentage scale. Therefore, the battery is charged up to the 85% level.