I have poor reception in my apartment. The coverage outside the building is 4 bars on both LTE and 4G (on average). Inside the apartment, there is no LTE and about 1-2 bars for 4G.
Poor reception means radio is working extra hard to seek and/or maintain connection. I tunred off "cellular data," kept WiFi on. I was still able to make/receive phone calls, regular text messages, and iMessages (through WiFi).
***don't forget that my regular 4G still struggled at 1-2 bars, but I still need it to function as a phone ***
On my first trial I got 9 hours of usage and 21 hours of standby (I'm pretty sure that "standby" is always elapsing even when the phone is used, so it is not 30 hours). The usage part was all-encompassing: games, video, phone, texting, browsing, downloading, music streaming, music playback, and anything else i'm forgetting.
Other important info:
Brightness is set bellow the letters T&N (looks like about 40-45%) and on 'auto'.
I do not use nor have any desire to use: iCloud, Bluetooth, Siri, Miscelleneous location services (other than "cell tower search"), Automatic Time Zone setting.
I have 4 email clients--2 of them push emails, 2 fetch only when I open the mail client.
I did NOT go "terminator" on Push notifications--refuse to give up functionality--BUT I do pick wisely which apps TRULY NEED to be pushed to notify me.
At the end of this test, I let the phone die (as per Apple Website). It took 1hr 55min to fully charge (from the wall)--this is very welcome news!
It is POINTLESS for me to keep "cellular data" on at home since my phone doesn't even load google.com without wifi--THANKS AT&T!!! But I do wonder how long it will last outside.
Can you post more details with your screenshots? It would be helpful for all of us to know what settings/usage yield what results.