my samsung galaxy plus battery draining quickly some time it is showing 50% but immidiatly 0% my samsung galaxy S plus battery draining quickly some time it is showing 50% but immidiatly 0% so please help me to solve this

ITS GINGERBOAT MODEL GT-i9001
yog
Not a lot of information but to venture a guess -how old is the battery? Batteries don't last forever.  What radios (GPS, Bluetooth and so on) are running?