ok, so I have my project working! The 18650 shield which has an advertised 1.5amp rating was very dim, and next to useless, I don't think it was providing the amperage advertised, or at the very least that figure is for spike draws and it should be running much less than that as a constant.
I wired in my mini360 buck converter powered by a 2 cell 18650 battery holder, and everything is exactly as it should be, no random characters on the LED displays anymore! Once setup, it's unbelievably simple, but finding information on how to do it in the first instance is no easy feat.