Original post by: James Macintosh ,
Make sure it's only shutting down when on battery power and not when it's plugged into a MagSafe adapter. Try reseating the battery connector. If it's still having issues when on battery power, then it sounds like something's wrong with the battery cells and they're unreliable. It doesn't happen often with new batteries but it does happen, I've seen then happen even with Apple's own batteries. I'd suggest asking for an exchange at that point.