Hydrometers come in two basic configurations. The first is called a calibrated float and the second is referred to as the floating ball. The floating ball hydrometer helps measure the charge in the battery. Some batteries may have a built-in hydrometer. However, this only tests the state of one cell. For an accurate reading, each cell must be tested individually. Over time, the balance of water and electrolytes in every battery becomes low. The floating ball battery tester will determine if the battery needs to be replaced.
Put on the safety goggles and rubber gloves. The acid inside of the battery is corrosive and can cause damage to the eyes or skin.
Disconnect the battery. Unhook the negative lead, then the positive lead from their respective posts.
Pry open the access ports on each battery cell to gain access to the liquid mixture.
Insert the floating ball hydrometer into one of the cells until the tip reaches the acid at the bottom of the cell.
Draw liquid into the hydrometer until the ball begins to float. Squeeze the bulb or pull up on the plunger depending on the model of hydrometer in use.
Write down the reading as indicated on the hydrometer and release the liquid back into the cell.
Repeat this process for each cell. Properly functioning batteries have no more than a 0.5 milliliter difference between each cell.
Add a few milliliters of distilled water to the cell that exceeds the 0.5 milliliter difference benchmark and test the cell again. Repeat this process until the cell reaches the 0.5 milliliter difference mark.
