Stephen, out of curiosity, what did your battery replacement consist of? Generally on phones after the iPhone XS you have to transfer the BMS from the old battery to the new one, and after the iPhone 11 you can no longer reset the battery health information without using what's called a tag-on flex board.
If you didn't reset the health information then the phone is still using the old data to judge the battery performance and will definitely not be accurate.
I am currently working with Alisha (@flannelist) on putting together as much information as we know about battery replacement on iPhones.
My understanding is that you are probably getting a pop-up warning that the phone can't be sure the battery is genuine or not, and a more extensive warning that appears under the battery information tab in Settings.
In addition, the Settings will be showing that the battery information is unavailable.
Here's how battery replacement now works as best I understand it.
If you still have your old battery, you will need to peel off the stickers covering the BMS, or Battery Management System circuit board and cut the circuit board off from the battery cell. You then have two choices; you can either cut the BMS off the new battery, or you can just buy a replacement battery cell that comes without the BMS. The original BMS then has to be attached to the new cell; the recommended method is spot welding but quick and careful soldering can work.
After that you attach a tag-on flex board to the battery (it goes between the battery and the logic board). Plug the whole thing into a device programmer such as the JC V1SE or the QianLi iCopy. Use the software provided with the programmer to reset the health percentage back to 100 and the cycle count to zero.
Finally, you have to install the rebuilt battery (new cell + old BMS) along with the tag-on flex cable into the phone. The tag-on flex is permanently installed in the phone along with the battery.
Outside of paying Apple to replace the battery, this is the only method I know of currently to replace a battery and have everything work correctly the way it should. Don't you just love Apple for throwing this crap in the way of a perfectly simple repair? As far as I'm concerned, the iPhone X is the last reasonably repairable iPhone there is; at least you can replace the screen and battery without jumping through hoops.
Here's a video showing the whole process being done on an iPhone 11 Pro.
iPhone 11 Pro AmpSentrix Core Battery Repair with Tag on Flex - YouTube
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