For years, my iPad 2 has gone nicely to sleep whenever I close the magnetic cover. (It's a Yoobao cover.) Battery wouldn't run down while it was asleep, and all was well. Now in the past couple days, although it seems to go to sleep when I close the cover (I need to type my passcode when I re-open the cover, even if the cover was closed just 5 seconds ago), still the battery runs down. If I leave it overnight, charge will go to zero. It doesn't seem like the battery is dying, because if I turn the iPad completely off and leave it off for a number of hours, there's no appreciable loss of charge. Any ideas what I can do about this?