that is due to ur brightness.......u should keep a black wallpapered theme......and turn to HD display resolution in the battery saver 2 mod............which would make ur phone cool and also long lasting...for about 6-7 hrs screen on time........and when u aren't need of calling anybody then u can turn on the flight mode on...........so as to get a screen on time of uptill 11.30 hr
Thank you for Joining Samsung community. We would recommend you to follow some troubleshooting steps in order to further isolate what you may be experiencing in your device. Find the troubleshooting steps on the provided link http://www.samsung.com/in/support/skp/faq/1119803. Please let us know what steps you have taken and if you have noticed any changes or improvements as this will help the Community to provide you further troubleshooting steps without repeating any procedure which you may have already followed. Be sure to hit ♡ when you find an answer that works for you.
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