Two Charge Moves for non-PvP Activities

I have not seen any information on this yet, but I am wondering how 2 charge moves behave in non-PvP activities. I have not yet given any of my Pokemon a 2nd charge move. I want to be sure that I determine what Pokemon are good for PvP first, at least. I recommend others wait too, as it costs a lot of stardust and candy.

For anyone who has a Pokemon with 2 charge moves (for science), do you have any idea how that works while a Pokemon is defending? What about when doing a raid or attacking a gym? Are players able to make use of both? Do they have to choose one of the two? Does the game automatically pick one (the original charge move)?

If the latter is true in any case, it would make it important to first TM the original charge move to your preferred choice. After wards you could pay the cost for the 2nd charge move, which would most likely see less use, except when facing its counters.