I thought about hard wiring power to my tank bag but decided against it. I've already got several USB power banks, the largest of which is 24,000mAh and can power all my USB devices for an entire day. For shorter rides, a 5000 or 8000mAh works well. I prefer my tank bag "untethered" and can be easily removed & locked in my top case, if necessary.
FWIW, SW-Motech does make an electrified tank ring for my EVO Micro Quick-Lock tank bag. That's probably what I'll go with eventually.
2014 K1600GT Sport