Replaced battery, iPhone crashes after a few minutes

Hi! So i recently got a battery to change the 70% original battery health on my iPhone SE. I am not sure what the problem is, but after connecting the battery and the cables on the logic board (and NOT putting the logic board or battery connector shield or the home button cables, so i did not fully close the phone,because i want to test if the battery works properly and if the phone works properly), powering on the iPhone seems to work properly and the phone works as expected. However, using it for roughly 3 minutes, the screen turns black, the iPhone turns off and then it restarts. When i wanted to check the battery health, it just keeps loading until it eventually crashes. the battery percentage also seems to not go down, until it crashes, then when it eventually restarts, it drops by about 5%. What might be the reasons for the crashes? Are the Shields for the logic board and battery needed for the iPhone to work properly? Is there a bug maybe that whenever the percentage number goes down, the iPhone crashes? I know these may be a lot of questions but i’m trying to troubleshoot this to the best of my ability. Any help is appreciated, thanks in advance!