How do I charge my iPhone 6 without it being on the whole time?
Plug the phone in to power
Then turn it off


If your charger is overloaded, faulty or your cable has issues, there could be an interruption of charge and the device will start up then. There's no way to prevent this necessary feature - it's a fail safe to turn on the device after replacing the battery or other system events that could cause the power to be low.