How can I restart STEVAL-MKSBOX1V1 when running on battery?

[ARami.2]

I am testing STEVAL-MKSBOX1V1 both connected via USB and running on battery using the mobile app. The device works perfect when connected via USB. However, it behaves in an unexpected way when running on battery. if I disconnect the USB when the app is running, the system continues working (this is what I want since I want to use the system on battery instead of cable). But if I close the app in the mobile, then the SensorTile.Box turns off and there is no way to turn it on again. I have tried using the buttons in the STEVAL-MKSBOX1V1, but they do not work. How can I use the STEVAL-MKSBOX1V1 on battery only in a way that I can close the app and restart it? Currently, the only way I have found to get a bluetooth connection is using USB. 

[JWu.12]

Hi, it should continue to work if you just exit and then enter again the smartphone app... Which application have you downloaded on the Sensortile.box? Are you sure the battery is full?

I have found a thread describing how to reset the board here:

https://community.st.com/s/question/0D53W00000LbrxoSAB/sensortilebox-nan-how-to-safely-recover-your-sensortilebox-in-case-it-shows-any-problem