No, a car battery cannot leak pure water. The liquid inside a standard lead-acid car battery is a mixture of sulfuric acid and water, known as electrolyte. If you see a clear, watery liquid leaking from your battery, it is almost certainly this highly corrosive and dangerous acid, which has been diluted by distilled water added during maintenance. Pure water would simply evaporate and is not stored separately. A leak indicates a serious problem, such as a cracked battery case from over-tightening hold-downs, physical damage, or internal failure from overcharging.
The primary risk is chemical burns and corrosion. Battery acid can cause severe injury to skin and eyes and will rapidly corrode metal parts it contacts, like the battery tray or nearby cables. If you discover a leak, prioritize safety. Do not touch the liquid with bare hands. Wear gloves and safety glasses, and neutralize any spills with a baking soda and water solution (it will fizz). A leaking battery often cannot be repaired and should be replaced. The leak also means the battery's internal chemistry is compromised, leading to a loss of cranking power and inevitable failure.
The following table outlines common causes and implications of a battery leak:
| Cause of Leak | Description | Consequence |
|---|
| Overcharging | Faulty voltage regulator causes battery to overheat, boiling electrolyte and cracking the case. | Permanent battery damage; requires replacement of battery and charging system repair. |
| Physical Damage | Impact from an accident or improper installation cracks the plastic casing. | Immediate leak and total failure; replacement needed. |
| Over-tightened Terminals | Excessive force on terminal posts can crack the case around the seal. | Slow leak; corrosion on terminals; eventual failure. |
| Case Failure from Age | Old battery plastic becomes brittle and can develop hairline cracks. | Sign the battery is at end-of-life; replace immediately. |
| Frozen Electrolyte | In cold climates, a discharged battery (low acid concentration) can freeze and expand, splitting the case. | Battery is destroyed; must be replaced. |
