I have a Mavic 2 Pro and use an Original Smart Controller with it, but, just in case, I bought a 'normal' controller as a back-up. I was going through all my records to update them ie. Drone serial nos. , Flight Controller nos. , Camera nos. , Battery Serial nos. etc etc....
I couldn't link the normal controller because the SC was still linked to M2P. I then found that if I made the SC the Secondary remote then I could link the normal controller to the M2P. Only one problem though on checking the menus I found that I could not see the battery information on the appropriate menu ie no voltages displayed nor other battery information, times charged etc.
Can anyone advise as to what I may have done wrong or something else that I may have missed?
Cheers for any input!

Did you go into menu on SC and choose the "Show voltage" option?

Yeah I did that Tony. I thought that was to show the batt voltage on the screen and that is ok. What I am missing is the battery voltages and charge times in the settings menu on the 'normal' controller. The SC is showing everything correctly.

Hi there. Can you please confirm what DJI Go 4 app version are you at right now? Did you try to uninstall and reinstall the DJI Go 4 app on your mobile device with the normal controller to see if the issue persists? Please provide us some screenshot showing the issue for us to check it here on our end. Please keep us posted. Thank you.

I'm gonna pile on what Paladin said.  Just download the latest directly from DJI's download site.  It definitely shows it all.

Good luck!!

Just a point, with the normal (non smart) controllers, the secondary has severely limited access to menus, I do not remember if this extends to battery info.

Sorry for not replying sooner. Tony, Sean and Dji Paladin, thank you for your replies and suggestions. I revisited the problem and have resolved the issue. I thought it might have been due to .the fact that I was trying to use an 'old' iphone (5s). Seemed to work ok in all other respects.
Anyway, I tried a more modern android phone which I also use for my 2 Mini 2s. (oneplus7t). I know Dji Paladin might step in here and tell me that both phones are not in the list of compatible phones but they do work! To cut a long story short, I found that the app downloaded from Dji centre was the latest but required a fly safe update, this was carried out and both phones now show all menus correctly.
So, 'finger trouble' on my part.