Thanks to all who have replied to this thread - I have held onto my iPhone SE2020 - having spent all the time switching over my content from the old phone, and backing up to iCloud etc it is just too much hassle to send it back. This table from Tom's Guide ( google iPhone SE 2020 battery life) explains it all - the size of the battery is inadequate completely for the size of the phone combined with the amount of processing power that Apple have packed into it. That is the simple reason that it cannot compete with bigger heavier more expensive Apple iPhones - or slower less powerful older ones.
The behaviour that the phone seems to exhibit for everyone, judging by threads etc.. is that it takes a while to settle into a routine of not losing charge catastrophically. I think Apple have been caught between a rock and a hard place... in the sense that they did their best to make a budget high powered phone which would appeal to those of us who loved the old iPhone SE... and we were seduced! But there needs to be some official explanation of how they could have brought out such an imbalanced phone.
It is simply not OK to bring out a new phone that has this kind of problem - even when it has settled down, the short time between charges, ie that it wont last more than a day even on minimal usage - is still a major flaw in the phone. And spoils it as a useful reliable tool compared with previous great iPhones - and more expensive ones such as the iPhone 11.
One hopes that the sophistication of iOS updates might improve things - but somehow I think those of us who bought this phone are stuck with it...
And I am speaking as someone who hardly ever watcheds Youtube or videos on my phone, uses it mainly to check email while away from my desktop, read text messages, uses the camera minimally most of the time, make minimal calls, look up infor on google, read the newspaer online and check news... -
My Screentime average is never more than 3-4 hours a day that is mostly spent reading ( mail, safari, texts, very few phone calls) - and it is still down to 20% by the early evening.. this is not a phone that you could rely on if you were working full time in business ( I am self employed and my job does not involve using my phone much).