In the upper right hand corner is a voltage display with a red background. (an alert) This is labeled “FC V” - and I’m guessing this is Flight Controller Voltage. Maybe it’s something else.
I checked my log file - and the POWR.VCC value never goes below 5V.
It makes an assumption about cell count and displays flight controller reported battery voltage divided by that cell count. The idea is to help you monitor multiple models without the mental gymnastics of remembering how many cells are in series. The behavior is configurable in the on-radio Yaapu config script.