How do I determine exactly which process is draining my battery? Every since installing Android 6.0.1, my phone runs very hot and my battery drains crazy fast.

With a little trial and error, I eventually determined that at least one process called AtFwdService was sucking the life out of my battery. However, even after killing that process, I still have periods of time where my battery drains rapidly.

I saw this question, though it seems targeted at Cyanogenmod phones, or maybe rooted phones. I have a stock, unrooted rom. In any case, I went with the accepted solution, to install an app called Watchdog, but it has revealed literally nothing. Maybe it needs root access to run properly.

I also installed Gsamm Battery Monitor Pro, and it tells me how hot my battery is running, what my battery drain projection is, and has nice graphs. But it also fails to tell me exactly what is draining my battery. For example, under "App Usage" it shows "Android System" as using 52%(!) of my battery. Clearly the problem is in there somewhere.

But, if I click on Android System, I see a huge list of installed packages. There's a "Manage" button which lets me act on specific packages, but none of the lists give me any indication of what package is the one draining my battery.

The default Battery Usage in Settings also tells me that the problem is somewhere in Android System, but says nothing more specific. In Developer Options, under Running Services, I see a list of running services, but these are not processes necessarily, and the list is not as complete as what's shown in the Gsamm app, so it seems I'm not getting the full picture.

Is there a way to find out exactly what process is murdering my battery?
Try the following:


Is the battery drain exclusive to your phone model? Some phones are innately more prone to excessive drain. Find someone with the same phone and do a cross comparison.
Battery capacity degrades over time. From experience, phones over a year do show a significantly lower overall battery life. The battery could be faulty as well.
Check external media. I have seen cases where an external SD card trips the Mediascanner, causing it to run excessively.
Check your running apps. My go to app when dealing with battery drain is BetterBatteryStats. BBS has extremely extensive features to tackle problems such as wakelocks.
Are your running a custom firmware? There are occasions where custom firmwares drain more battery then firmwares issued by the OEMs. 
Utilize the granular permissions to forcefully control rogue apps. Certain apps can silently access location or NFC functionalities.
Try a clean reinstall with stock apps and have it on standby for a full day. Check remaining battery percentage left afterwards. Use it as a control test to check if its the system or user app which is draining the battery.
Enable root and freeze system apps. Google applications and services, while often necessary, takes a good chunk of battery. Identify what you do not need and freeze them. Be warned, certain dependencies might stop your phone from booting.