Definitely rogue app running in background
even with 3g on n active email n fb refreshing overnite my most is 10%. Now averaging 3-5% over 7-8 hours
Check your apps n disable active refresh if you do not need it
Since you are new I will not ask you even to root it n use other methods to manage it better

just let the setting to be auto-channel 
cant... thats y i take the picture using another camera (webcam) cos if i save it as image/screenshot, banding wont be seen on other display... this is normal i guess? the banding in my picture?

not sure if me or u... i really do mean its about the banding, not the lcd/led/amoled display are made of based on their arrangement... just dont view the picture in 100% zoom cos i used an 8mp camera to get this (webcam)