No Power (Wont charge cable/wireless)

Replacing the battery would be the next logical step in trying to get the phone back to life. The fact that neither wired nor wireless charging works tends to discount the possibility of a problem with the charging port flex cable. It is still entirely possible that this is an issue on the logic board, but it would definitely be worth your time to try a new battery to see if that revives your phone.

So yeah if it was mine I'd just buy any aftermarket battery and see if installing it gets the phone working again. If it does, then you'll have to decide if you want to live with the Important Battery Message warning and the loss of your battery health information.

The easiest way to get rid of the warning is, of course, to pay Apple to replace the battery; naturally it's also the most expensive option. The self repair program is available, but it's my understanding that it's really not that cost effective.

Otherwise there are ways to get around those issues, but they're a major pain in the ass when all you want to do is swap out the battery. On your phone the battery is now paired to the logic board so in order to get rid of the bogus warning you would need to transfer the BMS, or Battery Management System - the small circuit board on the battery itself - to a new battery cell. That may or may not be feasible with your battery though; if it's the BMS on it that's failed then it won't do you any good to move it to a new cell since it still won't work there.

Okay, so assuming you successfully cut the BMS off the old cell and solder/spot weld to to a new cell, you're not out of the woods yet. Because even though everything will be working and you won't have that error message, the battery health information, which includes the health percentage number and the cycle count, will still reflect that of the old battery instead of being reset to 100% and zero cycles like it would be with a new battery.

On models prior to the iPhone 11, you could modify those numbers with a device programmer; just plug the battery in and it lets you set the numbers to whatever you want. However, Apple has continued their repair-antagonistic practices by encrypting the health data so it can no longer be updated by the programming tools.

However, the aftermarket manufacturers have come to the rescue here with something called a tag-on flex board. It's a tiny circuit board that gets plugged in between the battery and the logic board. It lets you manually reprogram the health information with a device programmer, but the catch is it has to be permanently installed in the phone in order to work.

So there you have it; a simple operation of replacing the battery is now a complicated surgery requiring replacing the BMS, adding a tag-on flex, and needing a device programmer. It went from being a $20 repair you could do yourself to costing over $100 in parts and equipment, at least the first time.

Needless to say, I am giving Apple zero stars for this "feature" - do not recommend.