Sam I correct in thinking that the M2P can only be controlled by it's dedicated controller and the current Smart Controller.
eg. You cannot download dji go4 app to the mini 2 controller and using that and a Smart phone to control the AC.

Hello there yogi053. Good day and thank you for reaching out. The DJI Mini 2 remote controller is not compatible with the DJI Mavic 2 Pro drone and vice versa. Thank you.

That is what I thought. Next question. How easy/difficult/impossible is it to replace Smart Controller battery when it starts to decline and not give enough flying time? ( Hopefully, not for a long while yet).

yogi053 Posted at 10-26 23:50
That is what I thought. Next question. How easy/difficult/impossible is it to replace Smart Controller battery when it starts to decline and not give enough flying time? ( Hopefully, not for a long while yet).

There was a video about this some time ago, but I am unable to find it right now. From memory, it is not so easy unless you are handy man with electronics etc.

kyalami Posted at 10-27 00:29
There was a video about this some time ago, but I am unable to find it right now. From memory, it is not so easy unless you are handy man with electronics etc.

Thank you kyalami. I will search for that video.

If you are interested there is a photo tear down here.  Not sure if it will help but thought I'd pass it along.  

Thanks for your input RDB.