Diagnosing and Reviving a Car Battery with a Bad Cell

A car battery with a bad cell can be a frustrating and potentially dangerous issue. However, with the right knowledge and tools, it is possible to identify and potentially revive a battery with a dead cell. In this comprehensive guide, we will dive deep into the technical specifications, diagnostic methods, and DIY solutions for a car battery with a bad cell.

Technical Specification of a Car Battery with a Bad Cell

A car battery with a bad cell may exhibit the following technical specifications:

Voltage: The voltage of a 12-volt battery with a dead cell may measure around 10.8 volts or less, depending on the number of dead cells. A healthy 12-volt battery should measure around 12.6 volts when fully charged, with each individual cell producing around 2.1 volts.

Specific Gravity: The specific gravity of a battery with a dead cell may be significantly lower than the expected range of 1.265 for a fully charged battery. A lower specific gravity indicates a low state of charge, which can be a sign of a dead cell.

Capacity: The capacity of a battery with a dead cell may be significantly lower than the rated capacity, as the dead cell may not be able to hold a charge effectively. This can lead to a shorter runtime and reduced cranking power.

Internal Resistance: The internal resistance of a battery with a dead cell may be higher than expected, indicating a lower performance and a higher risk of failures like thermal runaway. Increased internal resistance can be caused by poor contact between the current collector and the electrode material.

Electrode Contact Quality: Poor connection between the current collector and the electrode material that is rolled onto the collector can increase the internal resistance of the battery, which can be identified by low resistance measurements.

Insulation Resistance: Shorted batteries pose a serious risk of dangerous failures. Shorts can occur internally, but there is also a risk of external shorts when insulation fails or a battery is incorrectly connected to the pack. Verifying the isolation of the cell electrodes from ground and the insulation quality of any materials exposed to current can prevent a serious failure later.

It is important to note that these technical specifications may vary depending on the specific battery and the number of dead cells.

Diagnosing a Car Battery with a Bad Cell

To identify a car battery with a bad cell, you can follow these steps:

1. Measure the Battery Voltage: Use a multimeter to measure the voltage of the battery. A healthy 12-volt battery should measure around 12.6 volts when fully charged. If the voltage is significantly lower, such as around 10.8 volts or less, it may indicate a dead cell.

2. Perform a Load Test: Use a load tester to apply a load to the battery and measure its voltage. A load tester typically applies a load of around 150 amps for a period of 15 seconds. If the battery’s voltage drops below a certain threshold during the load test, it indicates that the battery has a dead cell or is otherwise defective.

3. Check the Specific Gravity: Use a hydrometer to measure the specific gravity of the battery’s electrolyte. A fully charged battery should have a specific gravity of around 1.265, while a discharged battery will have a lower specific gravity. If the specific gravity is significantly lower than expected, it may indicate a dead cell.

4. Inspect the Battery Visually: Look for any signs of physical damage, such as cracks, leaks, or swelling, which can be indicators of a dead cell.

5. Test Individual Cells: If possible, test the voltage of each individual cell in the battery. A dead cell will have a significantly lower voltage than the other cells.

By following these diagnostic steps, you can accurately identify a car battery with a bad cell and determine the appropriate course of action.

Reviving a Car Battery with a Bad Cell

If a car battery has a bad cell, it may be possible to revive the battery using a process called desulfation. Desulfation involves applying a specific frequency of electrical charge to the battery to break down the sulfate crystals that have formed on the battery plates.

To desulfate a battery, follow these steps:

1. Charge the Battery: Fully charge the battery using a battery charger to ensure that the remaining cells are at their maximum capacity.

2. Connect the Desulfation Device: Connect the desulfation device or a battery charger with a desulfation mode to the battery.

3. Set the Desulfation Parameters: Set the desulfation device or battery charger to the recommended settings for the battery type and capacity. This may include adjusting the voltage, current, and duration of the desulfation process.

4. Run the Desulfation Process: Allow the desulfation process to run for the recommended time, typically several hours.

5. Test the Battery: After the desulfation process is complete, test the battery’s voltage and specific gravity to determine if the battery has been revived. If the voltage and specific gravity have improved, the battery may be usable again.

It is important to note that not all batteries can be revived using desulfation, and the success of the process may depend on the severity and duration of the sulfation. If the battery cannot be revived, it may need to be replaced.

Reference Links

1. How to tell if a battery’s got a dead cell?
2. What is a dead battery cell, what causes this to happen and what are the implications?
3. Bring your dead batteries back to life | AnandTech Forums