Problem with battery around 50% on eu rom

I have serious problem with eu rom on Xiaomi 13 Pro (China variant) 1.0.12.0UMBCNXN .... when phone is charged to 80% and after using it for some time battery drops to 50% rhen phone gose off and after manual powering on battery indicator shows 1% and it works for several hours still showing 1%. Please help, because it's 2 weeks ol old phone and it's pretty anoying this 1%....
PS.: phone is just after bootloader unlock and clean install eu rom