All of the USB ports on our Flash Pro and Flash Pro Plus powerbanks have an automatic identification function, which means that when the device is connected, it can automatically charge the device without the need to press the power switch. This is an upgraded feature from our previous model Flash 2.0 as that required users to press the power button to turn on the charging mode each time before use and would explain why you have not come across this before.
As the original iPhone USB cable has an internal circuit, this means that when it’s connected to Flash Pro Plus, even if it is not charging any device, the iPhone USB cable is actually equivalent to a charging device. It can activate the DC circuit of Flash Pro Plus, thereby generating a loss, that is, 5V output as you have noticed on the display. Our testing has found that the iPhone cable is the only cable on the market with this characteristic.
To resolve this, we would recommend unplugging your iPhone cable after you have finished charging your device.
If this article does not resolve your issue, please submit a request and a member of our Customer Happiness Team will respond within 24 business hours.