So as of the past two months my Macbook has the tendency to go to sleep at random intervals if not plugged into the charger. I simply press enter and it comes back on. It has the tendency to do it multiple times and then not occur again for a few hours/days. It seems that when it does this once it will continually do it at that time until i either restart it or hook it up to the charger or put it up and get back on later. Seems very random. When the computer comes back on it has a X on the battery that quickly disappears. I've tried my gf's battery in her macbook and my cpu does the same thing. What could this be??? It only happens when it's not hooked up to a charger and to be honest at this rate it doesn't bother me THAT much but I'm afraid the frequency could increase over time. Any ideas what this is?