Yes, corrosion can absolutely drain a car battery. The white, blue, or greenish crusty substance that builds up on battery terminals is typically lead sulfate or copper sulfate. This corrosion acts as an insulator, creating high electrical resistance between the terminal and the cable clamp. This resistance forces the alternator to work harder to charge the battery and can prevent the battery from receiving a full charge. More critically, the corrosion can create a parasitic drain by forming a slight conductive path to the battery tray or chassis, allowing a small amount of current to constantly leak away, even when the car is completely off. Over days or weeks, this slow trickle discharge will kill the battery.
The primary cause of this corrosion is hydrogen gas released from the battery acid during charging cycles, which reacts with the surrounding atmosphere. It's more common in older, lead-acid batteries but can occur on any type.
Identifying and Fixing Battery Corrosion:
- Inspection: Pop the hood and look for the crusty buildup on the positive (red, +) and negative (black, -) terminals. The positive terminal is often affected first.
- Safety First: Always wear safety glasses and gloves. Disconnect the cables, starting with the negative terminal first to prevent short circuits.
- Cleaning: Create a paste from baking soda and water and apply it to the terminals. The fizzing reaction neutralizes the acid. Scrub with a dedicated battery terminal brush, then rinse thoroughly with water and dry completely.
- Prevention: After reconnecting the terminals (negative last), apply a small amount of dielectric grease or a battery terminal protector spray. This creates a barrier that prevents future corrosion.
For a quick diagnosis, here’s a table showing how voltage readings at the battery can indicate issues related to corrosion:
| Measurement Scenario | Normal Voltage (V) | Voltage with Significant Corrosion (V) | What It Indicates |
|---|
| Engine Off (Resting Voltage) | 12.4 - 12.7 | Below 12.2 | Battery is not holding a full charge due to resistance. |
| Engine Running (Charging) | 13.7 - 14.7 | Above 15.0 | Alternator overworking to overcome terminal resistance. |
| Voltage Drop Test (Terminal to Cable) | < 0.1 | > 0.3 | High resistance directly at the corroded connection point. |
Regular under-hood checks are the best defense. If you see corrosion, clean it promptly to avoid being stranded with a dead battery.
