What should you use to fill a battery cell to the proper electrolyte level if it is too low?

Distilled water is the appropriate choice for filling a battery cell to the correct electrolyte level because it is free from impurities and minerals that could negatively affect the performance of the battery. Standard battery electrolyte is a mixture of sulfuric acid and water, and the water needs to be as pure as possible to prevent chemical reactions that could result from contaminants.

Using tap water or any type of mineral or spring water introduces ions and impurities that could harm the battery's chemistry, potentially leading to reduced efficiency, increased corrosion, or even failure. Therefore, when maintaining battery electrolyte levels, distilled water is essential because it ensures the longevity and proper function of the battery.