I am 100% certain the battery drain in MJ7/MK2 is caused by connecting to WIFI networks in environments that have multiple AP's. i.e. once WIFI roams from one AP to another the battery drain starts. All my testing confirms this - consistently. I have actually tested being connected to one AP in a multiple AP environment for a long period and observed no wake locks on Android OS. Yet as soon I move to another location (i.e when I make it roam) the wake lock and battery drain starts. All this rubbish about clearing cache, factory resetting, nobbling your phone and so on are all stabs in the dark - It's the reboot that temporarily fixes it so people mistakenly put two and two together. So, if you use WIFI in a large building with multiple AP's try forgetting the network and not connecting to WIFI with multiple AP's. If you have already connected to a SSID with multiple AP's reboot your phone because once the battery drain starts it does not seem to stop until you reboot. You don't have to disable WIFI at all as scanning does not cause the wake lock. I have tested this thoroughly and so far I have not had any battery drain since not connecting to SSIDs with multiple APs. I can also back this up as I can create battery drain at will by simply connecting to a WIFI environment with an SSID distributed over multiple AD's.
My battery life is again fantastic and I am happy now that I know the cause.
Pretty poor testing by Samsung/Google as I see in past versions of Android Roaming has been an issue.