Battery critical with 90% charge

Hello, I am having a “coherency” issue with Nuki 3.0 smart-lock application.
From time to time it warns me that battery status is critical (<20%), even if the battery level is way above the threshold (I check it by entering the battery settings of the device).
What can be the issue?

If you are using the battery pack (1,2v) but the nuki thinks you are using alkaline batteries (1,5v), it might think the voltage is too low. Try checking this. Happened to me :stuck_out_tongue_winking_eye: