The electrolyte in car batteries is a mixture of water and sulfuric acid, and it plays a vital role in the battery's operation. The acid reacts with the lead plates to produce electrons, and the water helps to conduct the current between the plates. The electrolyte also helps to maintain the battery's charge and prevent excessive discharge, which can damage the battery or reduce its lifespan. Without the electrolyte, the battery would not be able to produce or store energy.