Wiring external hdd to pi with the +5v and ground to power bank, data pins to pi

I want to connect an external hard drive to a Raspberry Pi via USB, but the hdd draws too much power. Thinking of isolating 5v+ and ground from the hdd's USB cable, connecting it to a power bank, and only linking data pins between the Raspberry Pi and the hdd was wondering if there would be any problems. While i'm not sure, apparently i might have to wire the ground for the power bank, hdd and the pi's usb together?

Yes, the devices need to share a common ground.

also i'm using a wall adapter to power the pi if that's relevant

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And ALL devices have to share a common ground. Read https://en.wikipedia.org/wiki/Ground_(electricity)

so even the wall adapter too...

Read https://en.wikipedia.org/wiki/Ground_(electricity)