Recently I noticed that the battery on my iPad 4 is running down when the Smart Cover is closed. It's been fine for about 2 years. It was at 100% when I took it off of the charger at 7:30 this morning. Haven't used it and now I see that it's at 77%. This has happened a few times over the last week. Is there a setting that might have been changed. I haven't come across this before.