I want to supply a rpi3 + a high-current (up to 450ma) usb device portably. Is it ok to get a battery pack with two usb outputs, attach the rpi3 to it, attach the data end of the y cable to the rpi3, and the power end to the battery pack?
Or, is there a better way to do this?
I ask because I've read that Y-cables are not really part of the USB standard.
As a side question, am I correct to assume that it would not be okay to power the rpi3 through a wall plug, and a usb device with a y-cable and battery pack, since the two devices would not share a common ground?