pH is a measurement of electrically charged particles in a substance. It indicates how acidic or alkaline (basic) that substance is. The pH scale ranges from 0 to 14. Pure water has a pH of 7 and is considered “neutral” because it has neither acidic nor alkaline qualities. Alkaline water has a pH of 8 or above. Strongly alkaline substances, such as lye, can have a pH of 14. Acidic water has a pH lower than 7. Strongly acidic substances can have a pH of 0. Battery acid falls into this category.

Source: Healthline