OontZ XL - USB port will no longer charge other devices

Hi, this question is actually about the original OontZ XL (which is still a pretty terrific BT speaker, btw!).

The older unit still works great, connects easily, and plays music/audio very nicely. I’m just trying to figure out why the USB port on the rear panel will no longer charge other mobile devices. That built-in charging feature is extremely helpful when we travel; it’s always nice to know you have an extra power source around for phones/tablets!

Any ideas as to why the rear port won’t charge other devices anymore? Also, how do you open the case on this thing?!