I’m only half kidding. I’m a bit of a prepper and I have lots of powerbanks and devices that charge from USB but besides idling my truck I really had no other way to charge any of them in case of a long-term power outage which seemed a bit of an oversight on my part.
Not like this solves the issue. 30 watts (under ideal conditions) isn’t much but it’s a start.
Also be careful storing powerbanks at full charge, charge them at 80% or ideally around half for maximum longevity
It also saves a lot of money to do this. I’ve found it takes almost as much power to go from 80 to 100 as it does to go from 0 to 80.