Checking Electrolyte Level

WARNING: This page is about a different car, the 2004 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.

WARNING: Do not allow battery fluid to come in contact with skin, eyes, fabrics, or painted surfaces. After touching a battery, do not 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.

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

Fig 1: Removing Cell Plug Using Suitable Tool
Courtesy of NISSAN MOTOR CO., U.S.A.