External power

This is probably a no-brainer, but I'm quite a bit confused: I bought the Doorbell2 for my mother-in-law with the point given from the sales person, that it can be powered externaly. Since the manual doesn't state that explicitly, I called the German support. The lady told me, that external power will not suffice, the battery still needs recharging. This support page ([https://support.ring.com/hc/en-us/articles/115003495766-How-to-Connect-Your-Ring-Video-Doorbell-2-Directly-to-a-Low-Voltage-Transformer-Without-a-Pre-existing-Doorbell-](https://support.ring.com/hc/en-us/articles/115003495766-How-to-Connect-Your-Ring-Video-Doorbell-2-Directly-to-a-Low-Voltage-Transformer-Without-a-Pre-existing-Doorbell-)) says that it is possible, to power externally. What is the real fact?