Checking Electrolyte Level

WARNING: Never allow battery fluid to come in contact with skin, eyes, fabrics, or painted surfaces. After touching a battery, never touch or rub your eyes until you have thoroughly washed your hands. If acid contacts eyes, skin or clothing, immediately flush with water for 15 minutes and seek medical attention. Failure to do this may cause personal injury or damage to clothing or the painted surfaces.

Remove the cell plug using a suitable tool.
Add distilled water up to the MAX level.

Fig 1: Checking Battery Electrolyte Level
Courtesy of NISSAN NORTH AMERICA, INC.