With the flight pack in a large quad running 12S and utilising ESC Telemetry, I note that Betaflight reads in the voltage from each ESC and then averages them, however the reading is 25.5V even though I have 12S (50V) connected. However Betaflight also reports the battery voltage summary as correct, 50V which is normally used by betaflight FC for OSD. When using DJI Air Unit it seems to be picking up the averaged votlage which in Betaflight is incorrect. So two bugs here in my view, Betaflight ESC Telemetry with anything over 25,5V and DJI OSD telemetry using this voltage. Anyway, I wonder if someone could look into this issue, 12S is getting popular in bigger quads and smaller ones, but using it with DJI FPV you can't relaibly get the goggles to display the pack voltage, it's just stuck at 25.5V, my assumption is the 8 bit limit, 0.1 x 255 (8bit) and getting max reading of 25.5V.
Any assistance in getting this reviewed would be appreciated, or a fix for it. I am using a iFlight Succex-D F7 Standard flight controller powered from a 12V BEC, all works well except for this voltage OSD issue.

As a work around, have you tried enabling cell voltage and voltage in the Betaflight (custom osd) elements?

Yes, cell voltage is completely wrong and assumes I have 8S and then uses the voltage of 46-50V to determine a cell voltage of 6.3 max when reading the fully charged 12S! So weird.

Anyway I’ll test with this and I guess I can use the following to determine when to land, that is reading cell voltage as follows:

DJI OSD Cell Voltage x 8 cells = Actual Cells x Actual Cell Voltage

6.3x8=50.4=12x4.2
5.55x8=44.4=12x3.7
5.3x8=42.4=12x3.53

Based on this I would land at between 5.55 and 5.3 in the OSD, but a real pain it doesn’t support 12S

Just as a follow ups, I've checked through the Betaflight source code and it's not Betaflight with the issue, Betaflight has MAX_CELL_COUNT which is set to 8S for auto detection. Anything over that and you must force the cell count, that is use in the CLI force_battery_cell_count = 12, this then corrected the average cell reading in the OSD, so now I can fly safely knowing the cell voltage.

The OSD still reads the PACK VOLTAGE as 25.5V, even though checking through the code BTEAFLIGHT MNSP API that DJI would use to get the OSD information, the DJI air unit would read in the Battery Voltage which in my case is the combined average of the ESC Sensor readings, say 50V for 12S, this then obviously is well over the maximum that DJI can display, hence 25.5V is displayed in the OSD. Betaflight battery voltage is a 16bit number so no issues with it and force_battery_cell_count allows for up to 20S support.

SO the issue is with DJI Air unit or goggles for voltages over 25.5V.

I hope this can help anybody else having problems with using DJI FPV system with voltages over 25.5V, use average cell and force the cell count, then it all works for cell voltage in the OSD.

Cheers

This was very helpful, thanks fansdc11b173! Even setting force_battery_cell_count = 8 helped me getting a more accurate average cell voltage. The 25.5V issue is definitely on the DJI FPV system side as this was not an issue on my current setup when it was running analog. Hopefully DJI devs can see this issue and fix soon.