Everyone uses their device differently, so, unfortunately, there isn't any silver bullet. If there is, I haven't found it yet. I've done/tried most of the things I've listed below, and my battery life is pretty good. I'd say I'm a light to moderate user, and with the changes I've made on my phone (AT&T), I can go about 2 days with about 4-5 hours screen on time.
If your battery is draining that quickly, then it very well could be a rogue app or a bad battery. Look in battery statistics, and install GSam, and see if either point to any apps using battery or keeping your device awake.
You could also try some of these, if you haven't already:
You could be affected by the 'Wifi bug'. Connecting to routers/access points with a certain configuration (security) can cause battery drain. I was having this issue connecting to the wifi at my work, so now I have wifi and data both turned off when I'm at work, and only turn on data when I need it.
Disable 'always allow scanning' in Wifi advanced settings. I also have 'network notification' and 'auto connect' (this may be AT&T only) turned off
Turn off Enhanced LTE services (VoLTE) - should be under mobile data in settings
Turning off location can help, but if you need/want location enabled, disable just location history may help. Disabling location history will cause some features to not work, such as location specific reminders/prompts in Google Now, and location details in Fit.
Turn off voice activation in Google Now, if you don't use it.
Disable some of the S-Pen setting (ie. sound, vibration, alerts, pen detection)
You can turn off NFC if you don't use it, but I've never noticed any real difference with it on/off
If you have Google Fit installed, turn off activity detection in Fit settings. Even if you want this feature, you might consider only turning it on when you need it.
Disable any motions/gestures you don't use.
For apps, like Facebook, that sync, turn off sync and manually sync, or set to auto sync as little as possible. Or just uninstall Facebook and use the browser, or an app like Metal.
Go into your Google account (in Setting, accounts) and turn off sync for anything you don't want/need to sync.
Check to see if you're in a poor signal area. I believe GSam can show you a signal history.
Others have reported improvement using Package Disabler Pro to disable some uninstallable apps, particularly some of the Samsung apps (SFinder, SVoice, SHealth).
That's probably not a complete list, just what I can think of at the moment. For me, disabling Fit activity detection, Enhanced LTE services and location history had the biggest impact on battery.
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