Chosen Solution
My iPhone 6s Plus is completely dead and doesn’t show any signs of life. It will not detect on iTunes or power on. Battery is showing 3 volts, is that low enough to cause my issues? I have it completely torn down and motherboard shows no signs of abuse or water damage.
Could be a U2 Tristar charging ic chip gone bad which can be replaced by someone that offers microsoldering repairs. You can confirm this by getting a known good charged battery plugged into the phone and it should power on but not allow charging.
