But... Is this even possible? How exactly would it work?
Software. It’s all done in software. I suspect that they tell you you need the software to make the charger work. All you end up getting, besides the “back door”, is some fancy graphics that people can go Oh and Ah over. Now a USB port puts out 5v. I sometimes charge my iPhone on my laptop. No software on the PC is required. Which is good because I run Linux, and Apple (and M$) don’t make software that will run on it. This Energizer software wouldn’t work either.