Did you download the latest drivers manually from the link I provided above for the SB2? They are the May updated drivers (as mentioned by Cesar).
Before, I would lose 7% battery after shutting down. This is the battery report right before i tried to apply the fix:

As you can see, I shut down at 12:24am, and turned it back on at 7:32 and lost 7% battery in those 7 hours. This is even with the shift + shutdown but BEFORE updating the drivers.
After updating the SB2 drivers from the website I've these 2 battery reports:


These are all done with the SHIFT + SHUT DOWN option with the MAY updated drivers from this link:
https://www.microsoft.com/en-us/download/details.aspx?id=56261
And this has solved my battery drain while shutting down. Just for fun, tonight I'm going to just do a normal shutdown to see if the battery drain still remains (which I imagine will be the case). Then, tomorrow night I will test what Cesar mentioned about
turning off the option in the settings. I would much rather have my device retain 30% more battery on a Monday after a 2 day weekend of not touching it than to boot up 3 seconds faster on Monday morning and be at 50% battery.