Try to follow the instructions on this page in order to maximize your battery life:
http://osxdaily.com/2015/09/21/fix-ios-9-battery-life-problems/
https://www.apple.com/batteries/maximizing-performance/
http://www.idigitaltimes.com/ios-82-battery-life-problems-how-fix-quick-drain-is sues-iphone-ipad-and-ipod-422229
Try to reset your device. This won't delete your data stored on the phone.
- Press and hold the Sleep/Wake button
- Press and hold on the Home button
- Keep holding both buttons until the display turns off and back on with Apple logo on it.
You may also try to reset all settings: go to Settings - General - Reset - Reset All Settings
You may also try to follow these steps:
1. Navigate to settings/general/ battery usage. Check the applications. This will show you which app eats up your battery.
2. Turn off iCloud keychain: Navigate to Settings/ iCloud/Keychain / turn it off.
3. Limit apps activity on the background: Navigate to Settings/ general/ Background App refresh/ turn it off for each application which uses to much power.
4. Disable auto brightness: Navigate to settings/ display and brightness/ auto-brightness. Turn this option off.
If nothing helps take your device to the Apple Store for further diagnostics.
