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One of the most common problems with mobile devices is battery life.
New phones and iOS releases have been blamed in the past.
iOS 8 was particularly bad and there were a lot of complaints about iOS 10 also.
The iPhone 7 also got a lot of battery life complaints.

Common General Solutions for most situations:
Disable Background App Refresh.
Reduce screen brightness. 
Turn bluetooth off
Download maps in advance of a trip so navigation is not constantly updating them
  I turn off navigation until I get to tricky parts of a route.
Killer Apps: Spotify, Facebook Messinger, 
How to fix iOS 10 and iPhone 7 battery life problems | iMore
How to Fix Bad iPhone 6s Battery Life | GotTaBeMobile.com
How to Fix Bad iOS 10 Battery Life | GotTaBeMobile.com How To Calibrate iPhone Battery | Appledystopia Charging Why old Battery Lifes become sluggish over time | Macworld
last updated 16 Nov 2016