Thank you pickleMeTink, and yes, I concur with you that Apple Photos was indeed a very hungry battery vampire.
I'm exclusively mobile data and never use wifi as a contractual requirement. Location services are never on and I move between work locations with the phone switched off and in a Faraday Bag.
The phone only comes out of the bag and gets switched on if who I'm working with is comfortable with that and I am too. Then it's a secure core two server VPN connection to use encrypted email from the same stable as the VPN, password manager, back up drive and a couple of other apps. I thought initially it was this suite of highly security focused apps which were draining the battery together with Signal which could also be quite hungry.
However after being required by clients to cease using Signal or any other encrypted messaging I didn't notice much improvement in battery life.
When I was authorised to use the non Apple drive for photo back up and delete all iCloud back ups and all Photos data on the phone, things started to improve markedly. Same when Files data was deleted from iCloud and phone.
When iCloud back up was reduced to literally just manually backing up the barest minimum of the phone's system settings, (in my case 200MB and still some to shed soon), and every app was denied access to iCloud back up and mobile data use, that's when battery health improved exponentially.
The photo back up to the drive I now use is not two way synchronised, so zero background drain. I only very occasionally use the camera but when I do it's essential so unfortunately I can't delete Photos permanently even though it's kept empty. I have contemplated deleting it though after each use and only downloading it when it's required.
I have however deleted Mail and most other Apple apps and this has been a big part of the contribution to overall battery drain reduction.
Immediately following the iOS update, and for a depressingly long time after, I experienced a ludicrous 1% per second battery drain due to background system set ups which effectively reduced the phone to a state of complete uselessness.
This did stabilise eventually, but did not restore sufficient efficiency to enable normal and essential phone use.
Only the complete deletion of most Apple apps and the denial of mobile data access to all, albeit very few, remaining apps until absolutely required, enabled me to use the phone reliably again.
It still however requires a lot of power to use the VPN and few apps which must be used; so I'm even more minimalistic in my phone use now than my previous spartan usage. That's probably a very good habit to be forced to accept though.
