Really confused... hardwire ring 3

Hi, I have a ring 3 and have been using it on battery only but i appear to be charging all the time. I wanted to hardwire (and the box says battery or hardwired) but Im a little confused. So after watching videos etc, am i right in that it can only be hardwired if you have an existing door bell. If you dont you need to install a transformer with specific specifications. But ring doesnt sell the transformer? So where do i buy one for australian use. I see they sell a plug in power option, but how are people using this if the doorbell is external and your powerpoint is obviously going to be inside the house.