I purchased a new Dell XPS 13 and a new Bluetooth mouse because of the lack of USB cables.  I was very disappointed in the performance of the mouse.  I was not sure if it was the mouse or the bluetooth driver.  I would constantly have to move the mouse to keep it “awake”.  It turns out  it was a power setting that was quickly and easily resolved.  Turn off the power saving option for the bluetooth wireless and it started working right away.

Device Manager > Bluetooth > Intel Wireless Bluetooth