Battery draining within seconds I have a Samsung Galaxy S II GT-I9105. My problem is battery draining. It works normally after I charge it to full, but as soon as the battery percentage hits 30%, draining accelerates and will go to zero within seconds (literally).

But if I charge it and unplug at 12%, it drains normally again...

What is the problem? Should I buy a new battery?

Update:  I have bought a new battery and recalibrated but the same battery draining occurs
Try resetting your Android to factory setting and see if that helps. Otherwise I would suggest trying out a new ROM, as that helped improve my battery life considerably.