Yes, low water in a lead-acid battery is a common cause of a car not starting. The water in a battery is actually distilled water, which mixes with sulfuric acid to form the electrolyte solution. This solution is essential for the chemical reaction that creates electrical energy. When the water level drops too low, the lead plates inside the battery are exposed to air. This exposure causes them to sulfate—a process where a hard, crystalline coating forms on the plates. Sulfation prevents the battery from holding a charge effectively and significantly reduces its cranking amps (the power needed to start the engine), often resulting in a slow crank or a single click when you turn the key.
This problem is specific to traditional flooded lead-acid batteries, which have removable caps for maintenance. Sealed Absorbent Glass Mat (AGM) or gel-cell batteries are maintenance-free and do not require water refills. For a flooded battery, the plates should always be submerged under the electrolyte. If they're exposed, the battery can overheat during charging attempts, causing permanent damage.
Here’s a quick reference for symptoms and actions related to low battery water:
| Symptom | Possible Cause | Immediate Action | Long-term Solution |
|---|
| Slow cranking, dim lights | Low water level leading to sulfation | Check water level; add distilled water if low. Attempt a slow charge. | If charging fails, battery replacement is likely needed. |
| Clicking sound, no crank | Severely discharged battery; starter not getting enough power | Check terminals for corrosion first. Then check water levels. | Jump-start may work temporarily, but battery is probably damaged. |
| Battery case is warped or discolored | Overheating from low water levels | Do not jump-start or charge. The battery may be a safety risk. | Replace the battery immediately. |
| Rotten egg smell | Overcharging caused by low water levels damaging the internal structure | Ventilate the area. Disconnect the battery. | Replace the battery and have the vehicle's charging system checked. |
The best practice is to check your battery's water level every few months, especially in hot climates, and top it off only with distilled water. Using tap water can introduce minerals that damage the battery. If the battery has been low for an extended period, even adding water may not revive it, as the sulfation becomes permanent.
