Battery not lasting long + Computer shuts off unexpectedly

My MacBook Air's battery hasn't been lasting long for a while now, but it is getting much worse. It used to last 2-3 days, sometimes longer, when I first bought it and now I have to charge it 3 to 4 times a day. In addition if not connected to the charger the computer might shut off unexpectedly (does not give you a warning that it will shut off due to battery being low). I contacted the Genius Bar once and they said to clear something that I can't remember right now, which didn't help the issue. Cycle Count of Battery is at 663. Any suggestions to fix it? Or only a new battery will help?