An electrolyte is a substance that contains free ions and conducts electricity. An electrolyte is usually a liquid, most commonly a solution of acids, bases, or salts.
The acid solution in a vehicle battery is an electrolyte. It is typically one third sulfuric acid and two thirds water, and it completes the circuit between the metal electrodes inside the battery.
Optimum battery performance depends on correctly proportioned electrolyte. The condition of the electrolyte in a battery is usually measured using a hydrometer, a glass tube with a float and a graduated scale, which measures the specific gravity of the electrolyte.
In use, some of the water content of the electrolyte can sometimes be lost through evaporation, in which case the electrolyte can be topped up to its correct proportions with demineralized water. However, if the battery is tipped over and some of the electrolyte is spilled out, then it must be topped up with the correct electrolyte solution.
