Battery Fault Diagnosis

Battery Undercharging

Undercharging occurs if the battery is not receiving enough charge to return it to a full state of charge, this will slowly cause sulphation. This fault can occur if the car is being used only occasionally for short journeys, or for stop-start urban motoring. Undercharging will occur if alternator voltage is low (13.6-13.8volts), the alternator belt is loose or battery cables are worn and causing high resistance - If in doubt seek advice from an auto electrician.



1.  Voltage is below 12V (half for 6V batteries).

2.  Proportion is below 1.22.

3.  Difficult start-up, dim light, weak trumpet, abnormal usage of other electric apparatus in the car, such as acoustics.


Possible Reason or Cause

1.  Charging voltage regulator of cars has a low set point, or failure of charging system.

2.  Load of vehicles is larger than charging capacity.

3.  Slight short circuit.

4.  Engine failure.

5.  Starter failure.

6.  Bad contact of terminal wires.

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