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