It appears that users are experiencing some sort of huge battery drain bug in Windows RT 8.1 that is basically affecting all Surface RT tablets running the latest preview version of the operating system. This battery related issue popped up at the Microsoft forums and now it seems that a particular workaround solves the problem for many users.
At the Microsoft forums a new thread states that after installing Windows RT 8.1 Preview the Surface RT tablet experience huge battery drain when in Connected Standby. Losing approximately 30% of battery juice during the day and when the tablet is not being used.
The person posting the issue also details that using the powercfg /sleepstudy reports Microsoft UART V2 Driver (\_SB.UAR3) as being the root of the battery problem. Shortly after a community member suggested to enable the Bluetooth wireless radio on his Surface. Although, such fix sounds backwards, because we all know that it can waste even more battery, this workaround actually fixed the battery drain issue currently in the operating system.
If you are affected by the same problem try the following: from the Start screen use the +i keyboard shortcut, click or tap Change PC settings, go to PC & Devices, Bluetooth, and finally click or tap to enable the option.
The community member also detailed the reasons of this strange behaviour:
Powercfg /sleepstudy reports any issues that are preventing the CPU from entering its lowest power state during Connected Standby (e.g. screen is off). In this case, the state of the specific UART controller is preventing the CPU entering its lowest power state. This UART happens to be connected to the Bluetooth radio on Surface. Unfortunately, the bug that causes this bad state occurs exactly when the Bluetooth radio is turned off in PC Settings.
Apparently this isn’t an unknown issue for Microsoft in the preview version of Windows 8.1 on Surface RT tablets. The software giant will, on time, release an update to permanently fix this problem, but in the meantime, the workaround seems to solve the hiccup.
A strange story with a happy ending…
Update: If you are experiencing battery drain problems after installing the final version of Windows RT 8.1, Microsoft has recently published a new fix, you can find it here.