Hi Reuben -
OK - results negative on powering it directly off of 5 VDC and now it seems like the USB serial dies after a short time. It also feels a bit hot! So, I think I need to take you up on swapping the board. No magic smoke, but I think something has gone wrong!
I am quite sure I had it wired up right, but I did try having the USB and battery connected at the same time and maybe that damaged something.
Thanks!