iPhone 6 goes into boot mode

I purchased an iPhone 6 that had some water damage. The phone itself would continue to go through the boot loop and never actually restart.

The only way I could fix this is by unplugging the battery, plugging it into another device and charge for 30 seconds or so, then plug it back in and it goes through the loop and acts normally.

After that, the phone stayed on once until the battery died. Most of the time it goes back into boot loop once it goes into sleep mode and it always went into the loop upon restart.

I tried unplugging cameras, home button, and even replacing the wifi connector.

Any ideas?