Your DISCOVERY 3 PRO features reverse charging technology that allows it to function as a portable battery.
To use this feature, simply use the USB‑C cable provided with your device and connect it to your DISCOVERY 3 PRO; on the other end of the USB‑C cable, just connect the device you wish to charge.
When you connect your DISCOVERY 3 PRO to another device that supports this technology, an additional option will appear in the USB Preferences to choose whether you want the DISCOVERY 3 PRO to be the device that charges or to act as a portable battery.