If it can hunt down humans and kill them, it should be smart enough to know when it is about to run out of power and find a safe out-of-the-way place to recharge.
Of course, but a human would be the ones who could pull the plug on any charging device the robot decided to use.
Just not buying the threat of this thing, that’s all. Sure, a movie could be made out of it, but movies tend to be unreal anyway.