I have a 15 inch Mac Book Pro unibody. It's a couple weeks old. When it charges the battery it charges no problem and when finished the battery notification area of the menu bar says 100%. If I leave the lap top plugged in and use it while running off the adaptor the 100% gradually drops to 99 and than 98 and so on even though I am not running off the battery and the laptop is plugged in. It will continue to drop until I unplug the laptop and run off the battery for a while than plug it back in and it will than charge back up to 100%. Than it starts to drop again and the same thing all over. The machine runs great other than this. What is happening here?