My MBP started randomly shutting down when on battery power. If I take out the AC adapter, it'll run fine for a while before just turning off completely. No warning, nothing. The only thing is that this isn't the first time it's happened. I had this syndrome way back when I first bought the computer, sent it in, and got it fixed. And now, the problem's resurfaced. Any thoughts? My AppleCare expired - if I need to pay for a repair, how much do you think it will cost?