Sure, If you’ve purchased a combo pack the hub can be used as a power source for other devices such as your cell phone iPad ect. Plug the cable with the usb side into the hub and press the button on the side and plug to other end to the phone ect. it will draw power from you drone battery as a charger and will deplete the drone battery as it charges.
Thats how I discharge..With the Air2s, DJI included a little adapter that fits on the battery and lets you plug a usb device into it. I charge my phone and anything else with them to get back down to 60.
These ones are popular because they charge all the batteries at once. This is a trusted brand, affectionally known as the "YMCA" charger, due to the logo. These ones do not discharge the batteries down to 60%, but there is a switch you can toggle to charge them up to 60% or 100%. The one for the Mini also shows the charge cycle count for each battery.