Surface Pro 4 battery drain while OFF

It's good to hear there is some progress made on this issue.

The only thing I would suggest is turning of SP4 at a battery charge less than 100%. I say that because, as I stated before, it seem when the battery is charged to 100%, it might actually be slightly higher than that. So having turned off SP4 at 100% and finding out it still has 100% or 96% charge some 8-10 hours later could actually mean the battery has lost more than 0% or 4%.

I think it would be a more accurate test if you put it to sleep with battery showing less than 100%.

Just a suggestion.

After putting my SP4 into the first hibernation of a Windows session with the Device Manager setting change in place, with the charge at 100% going into hibernation, I powered it back on 9 hours later, and the charge was at 96%.  Before this discharge issue started happening on my SP4, it wasn't uncommon to have my SP4 off with a charge at 100% and then powered back on hours later or a day or days later with the charge at either 96% or 97%, so I'm going to assume that this is the same type of thing in this current instance.

This would mean that I've now been able to replicate what I did the prior day.  Now we're getting somewhere.  If the first hibernation of a Windows session (the first hibernation after a startup or reboot of Windows) has the Device Manager setting change in place already (with current firmware), the SP4 appears to hold the battery charge.  But then if another hibernation is performed from that same Windows session with the Device Manager setting already in place (i.e. not restarting Windows), the battery drain issue occurs.

The next test I'll try is to change the Device Manager setting back to what it originally was, then click "OK," then change it back to what I tried, then click "OK" again, then put the SP4 into hibernation again.  These changes will be made within the same Windows session without restarting Windows.  I want to find out if the battery drainage issue happens after all of this.  If the battery doesn't drain, then my hope is if it might be possible to come up with a script to run in which the script automatically performs these changes and then puts the SP4 into hibernation.  This would be an alternative method of putting the SP4 into hibernation instead of using the standard method such as via the power button (if it's programmed to put the SP4 into hibernation) or via the "Hibernate" option from the Start Menu, and this script would then ensure that the battery doesn't drain while the SP4 is in hibernation. 

Anyway, it appears that there may indeed be some progress regarding this issue, and that's a good sign.

Have you tried it with a full shut down?   I did the change yesterday around 8pm and checked it this morning at 7am and it was still at 100%.   I will let it lay for a day or 2 and see what it does.

I haven't tried a full shutdown yet, but I'll wait first to see what happens in your instance.  In my case, if the setting change in the Device Manager truly did make an effective difference, there was only one thing that was different in putting my SP4 into hibernation a second time.  Before the first hibernation, I made the setting change in the Device Manager, then rebooted the SP4, and then I put it into hibernation.  Before the second hibernation, the setting change was already in place, and I didn't reboot the SP4 beforehand (it was the same Windows session from the prior reboot before the first hibernation).

I do want to find out if I can replicate what happened in my case the first time around.  So I'll change the Device Manager setting back to what it originally was, reboot the SP4, then redo the Device Manager setting change, reboot the SP4 again, and then put it back into hibernation.