My iPhone always turns off once a week, please help

hello awesome members of applevis,
I'm seeking for a help, any suggestion, ideas and question are highly appreciated, cause my iPhone 5s are always make turn off once a week in no particular time and day, i have iOS version 10.0.2and only installed 16 apps to my phone and have 7.8 gig available.
do i miss something to configure? do i do something wrong in practice with phone handling or just an battery issue, i notice it since my iPhone are brand new. and the most frostrating part is it cannot be open by just pressing the power button on the top what i do is to press the home and the power button together, i do installed knfb reader, blind square, be my eyes, voice dream reader with James as voice, tune in pro, king of dragon pass, and etc. any intelligent idea member of applevis please!