Adding electrolyte to a car battery is a complicated subject, so it’s important to understand what battery electrolyte is, what it does, and why it gets low before you start servicing your battery yourself.
How Batteries Work – Adam Jacobson
When you hear electrolyte in connection with car batteries, people are talking about a solution of water and sulfuric acid. This solution fills the cells in traditional lead-acid car batteries, and the interaction between the electrolyte and the lead plates allows the battery to store and release energy.
That's why you may have seen people add water to a battery when the fluid level inside seemed low. The water itself is not the electrolyte, but the liquid solution of sulfuric acid and water inside the battery is.
When a lead-acid battery is fully charged, the electrolyte consists of a solution of up to 40 percent sulfuric acid, with the remainder being plain water.
