iPhone 6 Not Turning on, Not Charging, Can’t be detected by USB/iTunes

Hi,

While using my phone, my battery went down to 17% and I decided to charge it but my iPhone 6 suddenly didn’t charge when I plugged it in. Restarted it but it got stuck at the apple logo and didnt turn on ever since. Tried recovery mode but computer/iTunes won’t recognize it when it shows "connect to itunes" on its screen.

I went to my tech friend and we did some tests.

1. Opened it and checked the battery. Removed the battery and charged it with his charging board. Battery is good. It was charging.

2. Charged the battery for 2 hours and installed back to the iPhone, still wont turn on. Shows on screen "Battery logo" but didnt show the lightning cable/port on the screen so I’m guessing it’s detecting the lightning cable being plugged in its charging port.

3. We installed a working battery (from another iPhone 6), still iPhone wont turn on/coudnt be recognized by itunes/PC USB.

4. Checked charging port by connecting lightning cable to charging port and PC USB, tested for voltage/current on the board’s battery connector and confirmed that it had voltage/current on it.

5. Put my battery on another iPhone 6 board. Works perfectly fine.

With these tests, what else can we do? Any solutions? Any help would be greatly appreciated.

Please help.

Regards,

Paul