Ensure Your Device Has Enough Power
Before updating your iPhone, iPad, or iPod touch to iOS 11, ensure that your device is plugged in to a power source or has a full battery. The result of a dead battery during an update is never a good one – it’s possible you could end up with a bricked device. To avoid this, make sure that your iPhone, iPad, or iPod touch is plugged in and charging before updating to iOS 11.