I have the I Phone 7 Plus I did the ISO 13.5.1 update and have the same issues, battery drain, phone real hot, having problems making and receiving calls at times, cannot get e mails, some of my apps are not working.
I am off work with a broken foot and need my phone to still do work related stuff.
I tired the reset push top volume button once, push the bottom volume button once then hold upper right site button in till phone started up. Still have the same problem, Wondering if I need to erase the phone then reinstall everything that I have saved, how do I do this, if this is then next first of action? Please help desperate!