Do you have a Microsoft Surface RT tablet and are running Windows RT 8.1 Preview on it? If so, have you been experiencing battery drain in connected standby mode (a mode that keeps apps up-to-date, even when the screen turns off and locks, just like a smartphone)? For those who have not, lucky you. For those who have, there’s a fix from this Microsoft Community thread (hat tip to Neowin) that you can try.
What you’ve to do is to go to the command prompt (as an admin) and run the command 'powercfg /sleepstudy'. From the diagnostic connected standby report that’s generated, check if ‘Microsoft UART V2 Driver (_SB.UAR3)’ is listed as the culprit for keeping the device active. If so, the fix is simple: just turn on Bluetooth. The setting can be found under the Settings charm > Change PC settings > PC & devices > Bluetooth.
According to Arvind M., the person who suggested this fix, the offending UART controller happens to be connected to the Bluetooth radio on the Surface RT. And when Bluetooth is turned off, a bug will cause this UART controller to remain active, and thus preventing the device to enter connected standby mode properly. He also said that Microsoft is already aware of this issue.
Does this fix work for you? Feel free to let us know.
(By the way, this won’t work on the Surface Pro, as it doesn’t support connected standby.)