mi5 charge under 20

Hello, I've mi5 64gb. I was using MI5Global_6.10.13, had no issue with this matter. then I install xioami eu rom. now when my battery get low under %20 phone goes crazy. many errors, screen turn on of again constantly. after that I install the update, xiaomi.eu_multi_MI5_6.10.20_v8-6.0. its...