iPhone SE (2016) sudden battery drain and/or inaccurate battery level on 15.4.1

I suggest leaving the phone plugged into the power and connected to wi-fi for a couple of days, that way if my suspicion of some background indexing task using the battery and draining it should go away. I've been programming machines since 1974 and I am so upset at the quality of today's programming skills, what on earth they're teaching them these days, it's certainly not up to the level I've was taught.

Problem seems to have gone away as of last night, so if you've got this issue or similar wait a little while and it may clear all on its own. I reckon there's some indexing task or similar that's going on after system updates that whenever the phone is connected to Wi-fi uses a lot of power, this is NOT good. Apple please note: It needs to only do it when power is connected, that way it would not drain the phone's battery power and only do its tasks when connected to external power.

You sometimes need to have some patience with IT, a skill learnt over 50 years of working with IT. This is something that should have been sorted out by the programmers at Apple before the software was released so it never happens but the fix genuinely is to put the phone on power and wi-fi and let it do it's sync and that could take a couple of days as it did in my case. My phone is now working as expected and is 100% mobile but I had to have the required patience to get here.

Yes done that I also tried Restoring the phone to factory defaults and restoring from my most recent backup but that didn't work. :(