All i can say on battery life on Phone 2a is based on your wallpaper. When i go for HDR colourful hi-res wallpaper taken on this same phone as my wallpaper / lock screen I hardly get 1h screentime and full battery drains within 6-8 hrs.
I did change my wallpaper to a draker one and I did get a pretty decent screentime
This is default wallpaper which you get in Windows 11.
I don’t say this is a bug in Nothing phones but all I can say is AMOLED acreens are unpredictable and you can’t say how much exact screen time you are about to get in a charge.
Hopefully this helps many over here to check if there is really a software issue or hardware issues with phone 2a.