iPhone 7 Plus
I woke up to the new iOS 13 update on my phone. I was only able to use my phone for around 1 hour before the battery was around 20 to 30%.
Also, while using the phone the battery was heating up pretty bad.
Go to Settings –> Battery –> Battery Health and disable Optimized Battery Charging
It will take a very very long time for the phone to charge back up to 100%, but once that happened the battery life returned and the battery heating up stopped. If this changes I will update the post.