Nuki Opener, battery and usb operation

Maybe it’s just me, then I dind’t understand how to know if the Opener unit is operated by the battery or the usb 5V connection when both the battery and the 5V usb are operated in the same time. In the app I just can see the option to ignore battery warnings if Opener is operated by usb, so how can I understand which of the two is operated my unit in that moment? I could take off the battery and I also will do that, then my Opener is firmly installed on the wall and even if I follow carefully the instruction to open it to remove the battery, it seems really difficult to me without eradicating the whole unit from the wall, it is too firmly pressed and if I push the unit do not unblock the battery socket. My request for a future version of the Nuki app is to have clearly stated if the Opener is operated in 5V or on battery. For now I need help to understand this and to unblock the socket of the Opener to remove battery. Thank in advance for any help, if any.