If you absolutely have to make your Windows tablet battery last as long as you can, then knowing what drains its power will be very helpful. That's what Microsoft's new Sleep Study tool can do: generate a report of which apps and activities consume the most energy. Unfortunately, there's a catch -- it only works if your device is in InstantGo sleep mode. InstantGo, a feature for Windows 8.1, was previously called Connected Standby for Windows 8 and RT. Unlike other similar modes, it allows your system to sleep while updating apps in the background and keeps the device in a state that's quickly ready to resume.