I have Mavic Mini Fly more combo with the 3 batteries.
Flew few times without issues.
I have recently updated to latest firmware but not flown yet after update.
On the ground, all seams to work ok, with all 3 batteries.
What's the story on the need for batteries to be updated???
Some posts report the need to update firmware for batteries…
When and why is this applicable?

Hello and good day. Thank you for reaching out and for the information you have provided. The intelligent flight batteries of the DJI Mavic Mini needs to be updated so that the batteries will be optimized and will be able to cope up with the new features of the firmware of the said drone. Thank you and fly safe always.

DJI Stephen Posted at 1-7 08:19
Hello and good day. Thank you for reaching out and for the information you have provided. The intelligent flight batteries of the DJI Mavic Mini needs to be updated so that the batteries will be optimized and will be able to cope up with the new features of the firmware of the said drone. Thank you and fly safe always.

I have updated to latest firmware using the Fly App.
Strange there is no notification during update for the fly more combo users regarding batteries.
I suppose only one battery was updated during that update.
In the Fly App under "About" we can only check AC and RC firmware status.
Do I have to use the assistance software on my pc to check each battery seperatly?

Take a quick look at this thread.  It will answer your question easily.

https://forum.dji.com/forum.php?mod=viewthread&tid=205776

fans461cbed1 Posted at 1-7 10:14
I have updated to latest firmware using the Fly App.
Strange there is no notification during update for the fly more combo users regarding batteries.
I suppose only one battery was updated during that update.

Hi
You can follow post #4 (to switch off camera view at startup permanently) or follow these steps:

Once everything is ready (and the to be updated battery is in) click on the < symbol to get to the following screen:

Here, where the red text is written, the message about updating firmware of the battery will be displayed.
Hope this helps.

Thanks for your help guys!
I have updated my other two batteries in the Fly App
after disabling the auto camera view.
I haven't tried using the assistent software on my pc.
But I suppose this would also be the way to go?

just in case anyone else is reading, it is not necessary to disable the auto camera view to update the battery.  I updated 4 extra batteries w/o touching the setting.

The Saint Posted at 1-7 15:09
just in case anyone else is reading, it is not necessary to disable the auto camera view to update the battery.  I updated 4 extra batteries w/o touching the setting.

Correct.
I haven't been flying my MM after latest firmware update. Only bench testing.
While doing that I never returned to the screen with the blue "go fly" button. So I did not see that battery update notification.
That screen doesn't pop up when the setting is in auto camera mode.
You only get there when returning from camera view with the "back" button in upper left corner.