When an automotive battery is fully charged, the sulfuric
acid and water mixture will have a specific gravity of about 1.3. Specific
gravity is actually the difference in the weight of water in comparison to a specific
fluid. It is measured by a hydrometer. The amount of charge in the battery is
normally measured by the specific gravity of the battery. The specific gravity
of water is 1 and anything less than one is considered less dense while
anything that has a specific gravity of more than 1 is considered more dense
than water.
