Did you switch to Bluetooth headphones at some point? I've noticed battery performance is much worse when using Bluetooth, yet that is the trendy thing these days.
Nope. Always wired when the phone heats up like a frying pan. Playing podcasts does not drain the battery. Did not have the problem on iPhone 6, only noticed after switching to iPhone 7, and only really the last few weeks, but I see their support forum is full of complaints dating back a while.