Phone Problem (samsung D600e)

If you leave your phone charging when the battery is full, that will reduce the battery life. I think that is what happened to your phone.

Secondly, the batteries they sell here in Nigeria are fake and do not last long. (For example, the NOkia N91 batteries I bought in Nigeria can only play videos for about 30minutes, while the nokia n91 batteries I bought from the U.S can play videos for 6 hours) I suggest buying a new battery from the U.S. or maybe in a Registered Dealer of Phones here in Nigeria.