I have benefitted greatly from Google and XDA. So I thought I would provide a consolidated way of saving our battery's grace from Android System demonic drain.
I am running Euphoria with Furnace, and I had loads of Gapps installed.
I tried multiple attempts over a 3 days period and did many researches back and forth. And it came down to these few main culprits:
1. Android Location Services
2. Google Play Services
3. Qualcomm Location Services
4. Google Now Launcher
5. Unwanted Sync
Tools I have used to assist in this matter.
1. Disable Service - here
3. Privacy Guard (should be in built in most custom roms)
4. Titanium Backup
Basically the highest causing drain came from Google Play Services and Qualcomm Location Services. These items persistently wakes the phone up and runs on the background. Using greenify on there further cause issues as greenify tries to hibernate these services over and over again, making this a self-made draining routine.
I followed this thread on Google Play Services drain fix and used the Privacy Guard to perform those tricks. I ran through ALL Google Related Apps and as long as "Keep Awake", "Wake up" or "Auto Start" is enabled, I disabled them. I also look through apps I suspect were waking phone up by looking at the last activation of those events (Keep Awake, Wake Up, Auto Start).
Next I followed this thread on Guide to disable google play internal services using Disable Service app. I also took the opportunity to look at both 3rd party apps and system apps to see if there are services that could be disabled. I disabled Apex Notifier as I realize I didn't needed its service.
Then the next sneaky culprit was the Qualcomm Location Services. Even though I froze them with Titanium Backup, they persist in the system. So making a backup of them, I uninstalled them completely. Hasn't caused me any issue with GPS or Maps. They are namely, com.qualcomm.location and com.qualcomm.services.location. Both appeared as LocationServices 1.0 on Titanium Backup.
I went ahead to Greenify many Google Apps, namely Google App, Google Play Store, Google Services Framework, Google+. I also Greenify many apps that Greenify suggested would slow system down or appear to run in the background which I have no use for.
Lastly I uninstalled Google Now Launcher as it was persistently coming up as alternative home launcher even though I froze it. And I also went through settings of apps to make sure sync were turn off. I only kept Calender and Contacts and Gmail Sync on.
Now I have reduced Android System from 34% to 2% and increased my SOT from 2++ hours to 4++ hours at least. Not an out of earth SOT, but I believe that's decent.
Hope I helped and I wish you all the best in your endeavour to reduce Android System Drain. Cheers.