The wall charger brick that comes with the drone fly package is a USB-C PD charger. It is 18W and can charge at 5, 9, or 12 volts per the PD spec. Most assuredly it is charging at 9v 2A for 18W. When you use Mavic 2 adapter it is not charging at 13v, but most likely 5v. Just get a USB-C PD...