Electrolyte Solution is 65% water + 35% sulfuric acid

To achieve the chemical reaction that creates voltage in an automotive battery, the electrolyte solution inside the battery must have the correct mix of water and sulfuric acid. As you know, when a car battery is at 12.6 volts, it's charged at 100 percent.

At 12.6 volts, the electrolyte solution is 65 percent water and 35 percent sulfuric acid. This is the ideal combination!

Sometimes electrolyte "breaks down" and the acid moves onto the plates. So, there's less acid in the water. Whenever the percentage of acid in the solution decreases, the charge drops.