But I looked in the sound - music folder.
In there I have 02BTTL001 going up to 02BTTL41. And another one starting with 02BTTL001 going up to 02BTTL51.
These are one of the two battle music, that starts as soon you have deployed your troops, and the battle starts.
The one I linked to for the youtube video (chase) is called 01CHAS001 and goes up to 01CHAS058.
So by this I can only assume this is why Chase is not being played as battle music.
Any way around this? Is it possible to convert the youtube link into a .SAD and replace that as 02BTTL001?