My iPhone 6s will not turn on

The symptoms started when trying to charge the device. Sometimes it would charge and sometimes it would not. I already tried different charging cables and plugs, using a wall outlet and a computer USB port, I've tried a hard restart with the home and power buttons, I've tried to restore (with no power this is not possible), all to no avail. I finally purchased a new lightning port and installed it. It still will not power up. I have not tried installing a new battery yet and that is my last idea. Any other suggestions would be appreciated.