Please help

Idk if this sub is proper place to ask this but Since today evening I'm facing problems in my phone, My Phone is automatically being shutdown by its on and sometimes even powers on by its own and then again it repeats for some time, but sometimes it justs shutdown and doesn't power on back, So after that I power on myself it won't start fully and come to lock screen but second time only it come to lock screen and there's a large battery drain after powering on So What do you think must be problem? I think its battery but is it possible that there's some virus in my phone? Or is it hacked or something (I don't think so must be this)