Do you have the UNV battery pack? I had...an operator error...when I got one last week. If so, you plug into the same port on the side that you charge it with, not the one that says 3.7V out. Just connect it and flip the switch on the battery pack and it automatically switches the scope over the battery pack from the onboard batteries. Or you can turn the battery pack on and then the scope, same result and either way it should show the icon for using power from the battery pack.
Make sure it's charged, specific instructions in the box on how the to do that. Make sure it's turned off, plug it in at the pack and the wall outlet, then turn on the battery pack. It may take a few cycles of running it down and charging it back up before the light on the battery pack will turn green when fully charged.
This was the info given to me by Tyler at UNV last week when I called with those questions.