Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsBattery Diagnosis and ServiceHard
A technician is diagnosing a battery issue where the battery continuously overcharges, leading to a rotten egg smell and swollen battery case. The battery itself tested good initially. Which component is the most likely cause of this issue?
- ACorroded battery terminals
- BA defective voltage regulator
- CA faulty battery cell
- DA shorted starter motor
Show answer & explanationAnswer & explanation
Correct answer: B. A defective voltage regulator
The rotten egg smell (hydrogen sulfide gas) and swollen case indicate severe overcharging. The voltage regulator, typically part of the alternator, controls the charging voltage to the battery. If it fails, it can allow excessive voltage, leading to overcharging.
Why the other options are wrong
- A. Corroded battery terminals impede current flow, leading to undercharging or no-start conditions, not overcharging.
- C. A faulty battery cell would typically cause undercharging or inability to hold a charge, not continuous overcharging.
- D. A shorted starter motor would cause a parasitic draw and prevent starting, not overcharging.
Battery Overcharge Causes
Conditions or component failures that lead to a battery receiving excessive charging voltage, causing damage and safety hazards.
- Primary cause: faulty voltage regulator.
- Symptoms: 'rotten egg' smell, swollen battery, excessive gassing, electrolyte loss.
- Can lead to battery explosion and damage to vehicle electronics.
Memory trick: Overcharging makes the battery 'regrettably' 'swell' and 'stink' because the 'voltage regulator' is broken.