Error 21 after water damage

About few weeks ago my iphone water damaged. I have been trying to repair it since, after some time i got the phone on but it was stuck on boot cycle. After putting it into recovery mode i kept receiving error 21. I got some advice to replace the battery and i did twice.

The first time the phone recovered came on for a while then stated it was over heating, shortly after it died returning to the endless boot cycle.

The second came on for some time allowed me to make a call then died.

I am currently feeling like a keep getting so close then returning to step 1. Any advice?