First of all, yes, I have already contacted Apple Support via Twitter, but to them it's "perfectly normal" to lose up to 7% of battery overnight all of a sudden. My iPhone XR is 2 months old and its condition is perfect. This is definitely a software issue because the battery behaves normally, but it's just that something on iOS is causing a weird battery drain every now and then. My XR is currently running iOS 12.3, but this issue was present on the previous two versions.
I have gone through every single setting on my phone more than once and I am sure that there is nothing I'm doing wrong. This problem is not always present, but when it is, I can notice it not only when I leave my phone on standby overnight, but also while using it. A force restart sometimes does help, but it doesn't actually solve the issue. Turning off Screen Time and updating to iOS 12.3 have also temporarily fixed the issue, but it's back again.
Before I go to bed, I always turn off Wi-Fi from the Settings app (I never use Cellular Data at home), close all apps that are running in the background (if I haven't already), I turn brightness all way down, sometimes I turn on Airplane Mode (doesn't really help), I have disabled Auto Brightness, True Tone, Night Shift, Tap to Wake, Raise to Wake, Face ID and all Lock Screen notifications.
Aside from these options, I have also (completely) disabled the following:
-all sounds (including system sounds), vibration and haptic feedback, except for phone calls
-Bluetooth, Airdrop (receiving off), Handoff, Do Not Disturb, Screen Time, everything related to Siri that could be disabled
-all automatic updates (App Store, software updates), Background App Refresh (again, completely), Fetch New Data (applies to every app and simply everything that this feature covers) and analytics (iPhone and iCloud)
-all Location Services are completely disabled
-only 17 out of 64 GB used
-there is no way for me to ever consider turning off the animations (Reduce Motion), no matter what
There is probably something that I have forgotten about, but if I eventually remember something that I haven't mentioned, or if someone mentions it before me, I will make sure to reply or edit the post. Anyway, as I have already said, I have gone through all settings of everything that exists on my phone more than once, so I really don't know what could be wrong. Most people haven't even disabled half of these settings, yet they don't have any similar issues.
As about the actual draining issue (overnight), well, sometimes it's 1%, sometimes 2%, sometimes 5%, sometimes 7%, sometimes even 0%, but from my experience, it only comes down to luck.
The Battery category in settings reveals absolutely nothing about this issue because all it does is tell me which apps I have been using, and I already know that. I cannot see which apps were running in background and draining my battery while I was sleeping. However, there is one useful thing and it's Battery Health which says that my battery is at 100% capacity and that it supports peak performance which is true, but as I've already said, whatever is causing this drain is software-related.
Please, don't suggest me to perform a factory reset because that isn't even a real solution as it might likely not fix anything, and I can't be bothered with that right now. Not only that, but I don't have enough time either. It would take me at least 5 hours to set up the phone from scratch all over again because I like to adjust everything manually because of my own preference and the best performance, but sadly, this issue is preventing that from working as I imagined.
Worth mentioning, animations when opening and closing apps, swiping between pages on the Home Screen, and scrolling are sometimes choppy. When I mentioned scrolling, I know that it might sometimes take a bit to load up more content, but that's not the case. I'm talking about actual choppy scrolling, sometimes even in the Settings app. It's not that bad, but it's still there. Just like the battery draining issue, this also happens occasionally. Sometimes it just doesn't feel perfectly smooth and I find that a bit annoying. Don't get me wrong, it's almost normal, but it just doesn't feel like satisfying 60 FPS and it isn't so steady or constant.
Well, I guess that's it for now. I would really appreciate some help with this because I've been trying to find a solution for nearly 2 months (yes, that's how long I have this phone), but I can't find anything because most "solutions" online only work for people with no knowledge about technology.
Thanks in advance.