There are lots of app for android device to improve battery life. But you can easily improve your device battery life without installing any apps, just need to change some settings in your device.
1st change your account sync settings: – at first go to setting > then application setting> then accounts select
account which you need to modify disable some features which are not in use. If possible disable sync setting for those accounts which are not required.
Restricted background data
Disable background date: go to settings >then data uses > then more > restrict background data,
Restricted background data will stop some apps and services from working unless device connected to a Wi-Fi network,
Power saving mode: some of mobile phone have power saving mode like HTC M8 , galaxy s6,s5, & more turn on power saving mode if its available in your device.
Down display brightness level: try to set brightness level 25 to 30%. And also change your display backlight time for 15 seconds.
Update apps: keep updated your apps regularly.
Wi-Fi GPS:turn off Wi-Fi , gps, Bluetooth when it’s not in use.