I'll try to explain the situations as much as I can so maybe you guys can understand why it does this behavior. Just recently my battery just shut down when my battery charge was at 40% without warning. When I charge it, it says 0%. How did that happened? How did it drop 40% in a blink? I tried what others are saying here such as resetting the SMC with battery and AC adapter taken out and press the power button for 5 secs. That didn't work. I even calibrated the battery and that helps the battery a bit, but still shut down without warning. Is now a good time to invest in new battery? To help you guys, my macbook pro is 15" 2.33gHz and life cycle on battery is at 228. Thanks and any info will be greatly appreciated.