I'm curious where OP got that idea from too. Compared to full blown PCs sure the idle power draw is tiny, but it will still drain an average powerbank in a few days at most.

You could fully shut down the Pi (which would require some external hardware or user input to wake it up again) but even then compared to usual low power electronics drawing microamps in deep sleep, the milliamps the Pi slurps up is a lot. It would probably last a few weeks, maybe months in this state, but it would also take 30+ seconds to boot every time you need to do anything.