iPhone not charging once battery is fully drained

Hi Community,

Recently I was fixing an iphone 6 plus that had water damage, i took it full apart and cleaned it with isoproply and replaced the charging port, battery and screen. After that the phone tuned on and worked perfectly, however after a week the phone would not turn back on after the battery had been fully drained. I replaced the battery and this fixed the problem however now i am having the same problem but i tested the charging port and battery and both are working fine.