thanks thanks I really appreciate all of your replies :)) and it really feel so good, I mean atlst now I know that there is nothing to be worried. coz this thing is very new to me.. I mean I used to a device(not android) that the battery won't decrease it's batt. level even it's idle for weeks and even up to a month.
I've been attracted to samsung m31 coz it has 6000mah that's why I've been worried that my device might be defected and it's so hassle to return this unit although it's only 1day old haha so i need to observe and explore it more.
now im not worry anymore thanks to all of you who answered my question :))