About a couple months ago I did an in place upgrade to fix a couple of issues I had with Windows 10 and ever since then my CPU usage was always at 100% and when I click the batter tray icon the brightness button no longer says 100%, instead it just says 0% and it's grayed out and I can't click on it. My battery is draining a little fast not because it's defective but because of whatever is using my CPU, even when I turn on battery saver mode it doesn't help. And I tried booting into safe mode to see if the CPU usage would still be at 100% and it only goes down to 99%. I did another in place upgrade afterwards and it still didn't fix it.
I also posted this on Tenforums.com.