Most household batteries are acid-based. The acid is usually sulfuric acid, but can also be muriatic, phosphoric or nitric acids. The concentration of the acid solution varies by battery type; car batteries have a more dilute solution than do most household batteries.
The electrolyte in a lead-acid battery is made up of about 30 to 40 percent sulfuric acid and 60 to 70 percent water. In a fully charged cell, all the sulfuric acid is used up and only water remains. When lead sulfate crystals form on the plates during discharge, some sulfuric acid is released back into the electrolyte. That’s why it’s important to keep lead-acid batteries topped off with distilled water (not tap water) to maintain the proper level of sulfuric acid in the electrolyte.
Muriatic (hydrochloric) acid is used in some car batteries, although not as commonly as it once was. Phosphoric acid has been used in experimental zinc-air storage batteries. And concentrated nitric acid has been used as an electrolyte in early nickel-cadmium (NiCd) batteries and is still used today in some types of sealed NiCd rechargeable batteries designed for high power applications such as electric vehicles and cordless power tools..