Water plays a critical role in the electrochemical equation of a car battery. Although most car batteries are sealed and maintenance free, they do usually have a water level indicator that will allow you to observe if the water level is good. Low water level means the electrolyte will be out of balance and the battery cells will become too acidic resulting in sulphation on the battery plates. The non-conductive lead sulphate crystals will hinder flow of current through the electrolyte.