Disable Apple Music under Music app settings under General settings! Saves battery big time, then use music 3rd party app to stream for free. My favorite station 181.FM The BUZZ using the free "Radio Tuner" app that streams shout-cast servers.
Also disable background refresh for all apps manually and do what they need to do when screen is on!
One more if not using Bluetooth at all, turn it off and wifi if on celluar connection. If you need Bluetooth turn it on only when needed then back off. If your using IOS 9 it has new crazy auto brightness control, so disable it and set your brightness manually using the swipe up Control Center.
Also disable if you have the option manually under restrictions what apps can touch or use cellular data and which ones cant until your on wifi...
Siri eats battery so if you never use it, turn it off, turn off handoff settings to other apple devices if you do not use it, go through everything and turn off what you know you do not need for sure.
Also IOS9 drains battery on any device more than IOS8.
Also if you didn't, I would back up what you got on yer new phone so far through iTunes or iCloud, DFU install newest or older IOS9 build, then set up as new device and manually redo everything. I know on a phone this could be time consuming but it might fix problems.
Also you can do the battery calibration process which helped my new mini 4 gain 1-2 hours more in IOS9 without resetting anything. I did set it up as new device and manually got everything going on it like my older iPads.
There is a website that walks you through on how to calibrate battery on any Apple device. Also once fully charged to 100 percent you leave it on longer like 30 minutes or so, hit power and home button same time and hold them down until phone reboots to screen with apple logo, once you see logo let go. This deletes temp files, cached files, logs and anything else that could be causing a problem. Kind of like on Android when you erase the /cache folder and dalvik cache. Nothing will be reset, erased or deleted you put on it or setted up, its a manual way of cleaning things also to include the battery memory saved in a file I presume.
Once I did this, it went from 10 hours and 37 mins on my mini 4 in IOS 9 build 340 up to an extra hour of 11 hours and 37 minutes usage and now one more extra hour up to 12 hours and 20-30 minutes of usage with gaming and a lot of safari browsing. (been through 4 complete charges now) Mind you this is a wifi only new Mini iPad 4!