That is an interesting and important observation. But for me, the only time I really had a drain of only a couple percent over night was when I took out the SIM card. Airplane mode helps but doesn't really do much either. I don't care wether its draining 5 percent or 15 or 30 precent. This new device is not supposed to drain so much over an 8 hours period of standby. Period.
I have 3 out of 4 cellular bars pretty much all day and get about 80Mbit's down on LTE in the house. So there is no telling me that poor reception is causing the drain in my device. In your case perhaps having only 1 or 2 bars of signal could be contributing to the drain.
However, I am 99% certain, and mostly have been, that all this is an iOS bug or modem bug for that matter where some sort of process is not being put into standby properly but keeps running constantly. The battery drain curve shows it clearly. There is constant steady drainage like as if there is a load on the CPU/battery continuously. And it's not a curve that suggests that something is coming on and draining battery and stopping again. It is some sort of low power process that uses an average of 2% battery power per hour which also runs while you are using the phone. But if you are using it, it might drain around 10% per hour (of course depending on what you actually do) and this is where most people are oblivious to the drain (especially those that charge it every night) because who cares or notices wether the phone drains 10% or 12% in an hour while using it, right!?
But losing on average 18% over night while doing nothing, is kinda a big deal.
And I hate the suggestion that I simply put my phone on a charger every evening and don't worry about it. I don't want to do that. I want to put my phone down in the evening and wake up to close to the percentage that I had when I put it down. I don't want to think about wether I need to plug my phone in before I go to sleep. I just want to glance at the battery and know that when it shows 70% and I was able to go through the entire day, I can go through the entire next day without worrying to run out. (I should mention at this point that I don't use my phone all that much.)
I don't want to do the math in the evening that if I have 70% in the evening, calculating and accounting for at least 20% loss over night, that leaves me with 50% the next morning and contemplating weather that gets me through the day and wether to plug it in now.
My 2018 12,9 iPad Pro has magnificent battery life and it is running 14.3 too (iPad OS, but still) and I simply don't have to worry about it. That's the Apple user experience that people are paying for and what they should want and deserve. And finding justification and coming up with excuses as to why this 1300€ device just can't hold a charge is ridiculous. It makes me so mad, I can't even...
I am a passionate apple user since many years and I am still, but this just makes me so angry.
Are they even testing the devices and updates they release? And this iOS beta testing seems like an utter joke. Everyone can download and become a tester and still people complain about buggy software even though they are running a beta.
And there is minor and major updates being pushed out, which add fancy features that get hyped and praised (Fitness+, ProRaw, AirPods Max Support...) and they are completely forgetting about one thing. Bug fixes that actually solve problems in the software that millions of people use every single day.
Maybe the bug is still there to completely shred older devices and force people to charge so frequently which further degrades the battery, so people would finally give in and upgrade from their trusty 6S and get a new phone and to discover that even the new phone has the same problem. Big LOL. Ask me how I know
