Here is a bug that is in Windows 7. It may show up in Windows Vista and Windows 8/8.1. If your computer has a UPS backup battery supply, you may be unable to change the battery level in the power options. Here is how you fix that.
Press the start button and type “gpedit.msc”. Expand Computer Configuation. Then expand Administrative Templates. Then select All Settings. Search for Critical Battery Notification Level, Critical Battery Notification Action, Low Battery Notification Level, and Low Battery Notification Action. Open each one of these and choose a value you wish.