Killing batterys unexpected shutdown at around 50%

Hi I have a iPhone 6s plus that I have had to replace battery around 8 times as the battery works fine for around a month then dies at 50% like its flat pug it in I get 50% than continues till the battery is completely drained replace battery then like new for another month it's be like this since it was stolen from me and I got it back smashed now I'm about to replace the U2 Ic but I want to no if anyone knows of any other chips that can cause this so I can repair

Hi again I'm really stuck with this one I have replaced Tigris Ic mosfet ic tristar ic I'm unsure if it's fixed the shutdown issue yet but in addition to that I have released its going through power like nothing one hour YouTube video used about 30% so I looked at big pmic and found caps c2016 c2013 c2017 c2020 c2014 c2015 c2019 and c2021 all to be shorted can anyone help with this issue as I'm sick all I can think of it replace the pmic and no sines of water damage or corrosion gave it a ultrasonic bath