3 hours since unplugging my phone, and at light usage it's at 61%. It is the kind of problem I've had with my previous phone, and I have with my current phone, often starting a few months in and intermittently.
GSam indicates that app usage is 88% of it, with Kernel (Android OS) being 38% and Android System being 21%.
I know it is probable that "some apps" are using some OS functions and that would be the culprit.
Seeing it's a problem that hasn't been solved in more than a year, (even in Lollipop) I'm submitting it here so there's a definitive place to show the solution when it's found, instead of checking endless forum threads on XDA. (Hence note the answer must offer some kind of solution instead of "it's impossible")
I am not willing to take stabs in the dark such as disabling Google Now or Location tracking without a definitive proof. I have Wakelock Detector and it does not show anything unusual.
How do I definitely find out which app is responsible for the drain?
Battery draining fast because of Android System - Question regarding an HTC Droid on 4.4
How to troubleshoot overheating and high battery drain in an Android Device? - while thorough, does not address the share of the "Android System/OS/Kernel" items, specifically
Why do "android system" and "androd os" take 30% battery - accepted answer says "we're not there yet", I'm looking for the way or a workaround to get there
What can cause "Android OS" process to use high percentage of battery? - Is from 2011/Gingerbread and discusses possible example causes rather than a solution