Won't Turn on unless charger is plugged

The battery in your phone is likely at fault. A very strong indicator is that the phone only functions when connected to a charger. Once unplugged it powers right back off definitely points towards a battery issue in most cases. Seems possible the honor 6 does not have the most reliable batteries. I say this because I have helped others with the honor 6 that where having boot loop issues. The boot loops were caused from a failing battery that was not able to supply enough current to fully boot into the operating system. The batteries would only supply enough current to power on the device. It takes more power to fully boot into the operating system than it does to simply turn on the phone. That is why they were experiencing boot loop issues. The battery was failing and was not able to supply enough voltage. The sad thing is a lot of these people had taken there phones to a service center where they were told it was a motherboard issue. I recommended them try a replacement battery as I did not trust the service centers diagnosis and had a feeling they were trying to take advantage of people. I was correct to say that because most were able to fix their issues with a new battery.

So I strongly suggest getting the battery replaced. You may want to check out this post too.

Why after removing my charge mobile gets switch off