The electrolyte in a lead acid battery is a mixture of sulfuric acid and distilled water. Some batteries are sealed so the electrolyte cannot be checked. Refer to the owner’s manual or read on the battery to determine if it is a maintenance or maintenance-free battery. On maintenance batteries some of the water may evaporate over time.
Checking Battery Electrolyte/Adding Water. To check the level, take off your rings and watch, put on safety goggles and gloves, and then remove the cell caps. Shine a flashlight into the cells and inspect the level in each cell. Commonly a split ring indicator in each cell identifies the correct electrolyte level. Add only distilled water to any cell that is low, making all cell levels equal. Be sure the electrolyte covers the plates. Do not overfill. Replace the caps. Warning: Wash hands thoroughly to remove any battery acid after removing gloves.