Nokia 3120 Classic — Life of Battery

I have purchased my phone from Mahavir Enterprises NX , Near monis hotel, Thane (W) ,
Date of purchase 4/11/2008 ,
The problem of Battery started few weeks back the battery gets exhaust very fast and is under warrenty Period , Nokia (Prudent Service) Ph:[protected] recommend me to get a new Battery from other dealer because they are not having battery of it though it is under warenty period.

Please look into the matter and Help me,
My Res Ph:[protected].