My battery life off the bat was a little disappointing - I had just come from a 2014 moto X, and the Z3C got about the same battery life - 4 hours SOT across ~14-15 hours.
A factory reset, and a lot of troubleshooting/tweaking later, I finally managed good battery life today - 6 hours 15 min of SOT across 32 hours. Hopefully it will keep improving!
Some things that helped me get better battery life:
1) cleared cache and data for google search app and google play services app
2) hooked up to computer and watched adb logcat while z3c was locked and asleep - saw errors coming from the yelp app (error connecting to gmaps again and again), and prevented the phone from deep sleep.
3) i had android device manager disabled in settings->security->device administrators, but in the "google settings" app icon, it was still enabled to report location. disabled that.
4) turned on stamina mode, stamina clock, enabled queued background data, whitelisted instagram/messenger/gmail.