move AG database files between disks
Took me some time to test it but this actually works.

Step 1

Add the new disks to both nodes of the SQL Server Availability group

Step 2

Stop the SQL Server service of your passive node

Step 3

Move the SQL Server database files from the old disk to the new disk

Step 4

Adjust the drive letter of the original disk to another letter using f.e. diskpart

Step 5

Rename the disk where you move the database files to to the drive letter of the original disk

For Example= Old disk D: --> renamed to F:  New Disk E:  --> renamed to D:

Step 6

Restart SQL Service on Passive node and wait untill everything is back into sync.

Step 7

Failover to the passive node &amp; do the exact same process on your previously active node.

Downtime?

If you follow this process you will have no downtime, except for the failover of your availability group.