Hi! This is what I get when I Google your error code?????
http://www.bleepingcomputer.com/forums/t/493895/error-code-800f0900-windows-update-failure/
There is also a trouble shooter in W7. Not sure but would assume W8 also has one. Looks like you're are gaining on your problem. Keep me posted. Not sure about the battery. I don't think it is relavent?? Now would be a excellent time to create a back up image of your OS on a external devise:smileyhappy:
Dokie!!