Checking Electrolyte Level: Sulphation
WARNING: This page is about a different car, the 2005 Infiniti FX45 and 2005 Infiniti FX35. However, it is still accessible from the selected car via links, so may be relevant.
A battery will be completely discharged if it is left unattended for a long time and the specific gravity will become less than 1.100. This may result in sulphation on the cell plates. To determine if a battery has been "sulphated", note its voltage and current when charging it. As shown in the figure, less current and higher voltage are observed in the initial stage of charging sulphated batteries.
A sulphated battery may sometimes be brought back into service by means of a long, slow charge, 12 hours or more, followed by a battery capacity test.