COPY - Mixi Sling Bag w/USB Port - 687 $35 or $30 w/offer

This Mixi sling bag with USB port is great for the techie guy or gal. I think it may have originally had a battery pack but when I bought it, I did not see one. I am though not sure how it would charge devices. The bag does have a plug connected to it but that is all that I know about it. I looked up the bag online and just got more confused as the plug inside as I see is the back part (see photos). The bag is in excellent condition however. If you are familiar with this bag and can share what you know about it, please do so in the comments. Thank you 😊