I bought my iPhone 13 Pro Max a month ago and have been using heavily the past month as a hotspot. Up until a couple days ago it would generate a little heat but not a lot like it does now. I noticed when recharging a couple days ago it stopped at 80% and didn't trickle up to 100% like all the help says it will. For about eight hours it was stuck on 80%. I rebooted it and that seemed to work then it froze again about an hour later and only about 83%. I unplugged it and let it cool off for about an hour then tried again. It was about midnight now and was slowly trickling up, plus I had turned the battery optimizing feature off.
The next day, yesterday, it was finally at 100% when I woke up and quickly discharged in a couple hours back down to 1% and was started the recharge cycle over again. I normally get at least 4-5 hours off a recharge when using as a hotspot but not this time, plus it was insanely hot to the touch, much hotter than normal.
Again I started the recharge cycle again and turned the battery optimize feature back on. It quickly recharges to 80% but then freezes again. This time I turn it off manually and let recharge overnight and it was at 100% this morning. It's still much hotter to the touch than previous.
I've got the latest update iOS 15.5 and all my apps are up-to-date and so forth. I only use the Apple charger and cord and I only leave plugged in to recharge.
I have an Otterbox Defender case but normally I couldn't feel the heat like I could the few days before I got the case but now even with the case it's much hotter than without.
I don't have a problem with it in my car because I have an air-conditioning vent blowing on it and I don't leave it in the car nor do I have it in sunlight, so all items for the car problems don't apply.
Other than the very few car trips, it's only used inside an air-conditioned home away from any heat source, directed sunlight, other electronics, etc, so all those items of concerned are checked off also but still it's overheating like crazy and discharging the battery much faster than usual.
The only thing I've done different that I can think of that may be the problem is I added some other devices to the Bluetooth list because it was after that I started having these heat and discharge issues. I've removed those devices and reset all settings but it's still overheating and over discharging.
I've tried looking for an app to diagnose this but can't find anything other than the usual hard drive cleaners and such.
I've done everything but a factory reset and that's something I don't want to do if a simple solution could be found instead.
Sorry for the long comment, I was just trying to put everything up front to avoid the back and forth with further questions and replies to what I've already done.
If you need any further information, please don't hesitate to ask.