How do you check specific gravity of acid in a car battery?

To check the specific gravity of acid in a car battery, you'll need a hydrometer. First, ensure the battery is fully charged and then carefully remove the vent caps. Insert the hydrometer into the electrolyte solution, squeezing the bulb to draw in the liquid, and then release it to allow the float to settle. Read the specific gravity measurement on the scale; a higher value typically indicates a fully charged battery, while a lower value suggests it's discharged.