In a matter of a week or two I upgraded from UI 5 to 6 to 7.
The move from 5 to 6 more than halved my battery life instantly.
In one go my phone went from lasting about a day and a half roughly, to needing to be charged by just after lunch time. Absolute disgrace.
So then I upgraded again with all the promises I'd read that it has improved performance and battery life and it's dropped at least by another 15%.
My phone is lucky to make it to lunchtime now, thanks to these upgrades.
This is how I do it. I don't let it move my files.