What does a higher specific gravity indicate about a battery?

A higher specific gravity reading in a battery is a direct indicator that the battery is fully charged. Specific gravity refers to the density of the electrolyte solution in a lead-acid battery, which is largely composed of sulfuric acid and water. When the battery is charged, the concentration of sulfuric acid increases, resulting in a higher specific gravity. Normal, healthy batteries, when fully charged, typically show higher specific gravity values than those that are partially charged or discharged.

In contrast, when a battery is discharged, the specific gravity decreases due to the dilution of sulfuric acid as water is produced from the chemical reactions taking place. Therefore, a measurement of lower specific gravity would indicate that the battery is either partially discharged or could even be in a state of failing. Thus, understanding the relationship between specific gravity and state of charge is crucial in assessing battery condition and performance.