Welcome to the party. Just joking.
My i5 128GB SP4 is also experiencing battery drain after full shutdown. Mine is about 4-5% per 24 hour period.
I've tried pretty much everything under the sun including full reset.
At this point, I see no hope.
I have a very similar setup.
I do occasionally lose connection to my monitors but that's rare. Lately though, I do lose network connection if my SP4 is locked for more than a few minutes. It wasn't like this before, but seems to have started recently.
I have Windows Hello facial recognition set up.
After the latest update (1809), when I boot up my SP4, I get a message saying "Something went wrong. Please sign in with you PIN".
At that point, I can type in my PIN to log in or I can click on the sign in options and choose facial recognition...
Do you have fast startup disabled on your Surface Book? I remember vaguely that I had to disable that AND use the full shutdown command to minimize the battery drain while being shutdown.
I kind of doubt you have the fast startup disabled and if so I'm really puzzled on what is causing this...
So I did another test by shutting down my SP4 at 84%. Today I powered it up after about 20 hrs and it had 81%.
So mine is not as bad ad jeffrodrig's machine but certainly not ideal as it really shouldn't lose 4-5% battery every 24 hours after a full shutdown and nothing is using energy.
I did another test by shutting off at 90% battery. Turning it back on after 26 hours the battery was at 86%.
So it lost 4% over 26 hours and I guess that is acceptable. I wish it lost less but better than losing 5% over 6 hours like jeffrodrig's battery.
The UEFI firmware version I have is: BIOS Version/Date Microsoft Corporation 108.2318.769, 8/14/2018
I do want to stress that I am using the "Full" shutdown command as shown above so I'm not entirely sure if that is preserving my battery life after the shutdown or the new firmware.
I've done all the latest update and used a shortcut to "C:\Windows\System32\shutdown.exe /s /f /t 0" to shutdown and after 24 hours the battery was still 100%.
I did notice the shutdown and startup takes a little longer but not enough to bother me.
So I'm happy with the result.