A technician is inspecting a conventional lead-acid battery and measures the specific gravity of the electrolyte in one cell as 1.200, while the other five cells read 1.260. The battery's open-circuit voltage is 12.4V. What does this indicate?
- AThe battery is healthy, but needs a full charge.
- BThe battery is undercharged, and one cell is shorted.
- CThe battery has a shorted cell, and likely needs replacement.
- DThe battery is fully charged, but one cell is weak.
Show answer & explanationAnswer & explanation
Correct answer: C. The battery has a shorted cell, and likely needs replacement.
A significant difference (0.050 or more) in specific gravity between cells indicates an internal fault, such as a shorted cell or a dead cell. A specific gravity of 1.200 is significantly lower than 1.260, confirming a fault in that cell. A battery with a shorted cell cannot be reliably recharged or load tested and typically requires replacement. An open-circuit voltage of 12.4V (75% charged) combined with a bad cell also points to a compromised battery.
Why the other options are wrong
- A. The specific gravity imbalance clearly indicates a fault, meaning the battery is not healthy.
- B. While the battery is undercharged (12.4V), the specific gravity difference directly points to a shorted/dead cell, which is a more severe issue.
- D. 12.4V is not fully charged, and the cell difference indicates a fault, not just weakness.
Shorted Battery Cell
An internal fault in a lead-acid battery where the positive and negative plates within a single cell make contact, leading to a loss of voltage and capacity in that cell.
- Causes significant specific gravity difference between cells
- Reduces overall battery voltage by ~2 volts
- Battery cannot hold a charge effectively
- Requires battery replacement
Memory trick: Uneven gravity, cell's gone faulty.