Each battery needs to be updated. Turn off RC2 and device, put battery in device, turn on RC2 then update firmware; repeat for each battery. Doing this for the A3S and RC2 at this time, Next I'll do it for the RC 2 Pro and Mavic 4 Pro...
If -40F sounds chilly, we've had -70F at our home but thanks to global warming that never happens anymore, so please, continue burning fossil fuel as much as possible and consider raising cows :).