Why is my phone dying so fast?

Hi ghosty,

I agree with @shingle that you're looking at a battery issue. If it's been 8 months you should check your warranty for the Battery and Bulbs repair and see if it's still good (iFixit batteries are warrantied for a full year). If it's still under warranty then it would be worthwhile to take it back and have them replace it again, which shouldn't cost you anything. You never know, no matter how good your supplier there's always a chance you get a bad battery in a batch so I'd give them at least one second chance.

Otherwise you could always opt to replace the battery yourself, but Apple has decided to make that process far more difficult than it needs to be. Here's the guide you'd use to do the job.

iPhone 11 Battery Replacement - iFixit Repair Guide

The battery replacement itself is no more difficult than it has ever been on an iPhone, but as of the iphone XS, Apple has started pairing the battery to the logic board. That means there's a software lock that matches the two and if they don't match you'll get a pop-up warning for the first couple of weeks to the effect that your battery may not be a genuine Apple battery - even if it is a genuine Apple battery. It also means the battery health information will no longer be available; an important diagnostic that gives you an indication of when to replace the battery.

The only way around this if you're not an Apple authorized repair center is to remove the BMS circuit from the original battery and transfer it to a new battery cell without a BMS on it. You then have to use a device programmer such as the JC V1SE or the QianLi iCopy to reset the health statistics (percentage and cycle count) back to 100% and zero, respectively.

If that by itself wasn't bad enough, as of the iPhone 11, they changed the way health statistics are kept on the battery so the device programmers can no longer read and write that information. So you can still keep the original BMS, but it will still be showing the old outdated health information instead of being reset due to having a new cell installed.

The aftermarket industry has come to the rescue here, though, and created something called a tag-on flex cable; it's a tiny circuit that plugs in between the logic board and the battery and allows the previously-mentioned device programmers to once again clear the health information. You plug the tag-on flex into the battery, then plug the assembly into the programmer and clear the stats. Then you install the battery with the tag-on flex into the phone, leaving the tag-on permanently installed in the phone with the battery.

If that all sounds like too much work to be worthwhile for a battery replacement, you're right - and that's exactly what Apple wants to happen. That way they are the ones to do the battery replacement and get paid for it. They get to charge what they want for their battery and their labor.