Battery electrolyte is the liquid substance found in most car batteries. It is sometimes called battery acid because it is very acidic. In fact, battery electrolyte is a mixture of water and sulfuric acid.

When the electrolyte level in your lead-acid battery gets low, you may wonder if you can use a common electrolyte alternative, such as salt water or baking soda. Don't. Never put electrolyte in a lead-acid battery.

If your battery's electrolyte is low, the only thing you should ever need to add is plain water. There are some specific circumstances where sulfuric acid can be added, such as if the battery has been tipped over and is leaking, but never add anything else.

When your mechanic tells you that your battery’s electrolyte level is low, it means that the fluid level in one or more of the battery cells has dropped below the top of the lead plates. What does that mean? Car batteries consist of a series of lead plates that are immersed in a bath of water and sulfuric acid. This creates a chemical reaction that builds up electrons, which are eventually discharged as an electrical current.