Cant you use “%~dp0” ??? 

Some more information: https://www.geoffdoesstuff.com/windows-batch-scripts

in sysprep xml file how we can define ?

we use sysprep during vm build so it will pick D drive by default for sysprep cidata so i need to make changes

Maybe I'm missing the exact issue here. 

You have a virtual machine with 2 disks???

And the second disk is added as the drive??

And you want that drive to have a different drive letter??

You should be able to run custom scripts from the unattend file, 

If the drive isn’t a local disk you would need to mount/connect to where the scripts are somehow, unless I am also missing something from your question. 

Also I have not had to time mess around with this much but OSDCloud looks very interesting.