How to change current working directory using a batch file
Specify /D to change the drive also.
CD /D %root%
Just use cd /d %root% to switch driver letters and change directories.
Alternatively, use pushd %root% to switch drive letters when changing directories as well as storing the previous directory on a stack so you can use popd to switch back.
Note that pushd will also allow you to change directories to a network share. It will actually map a network drive for you, then unmap it when you execute the popd for that directory.
Try this
chdir /d D:\Work\Root
Enjoy rooting ;)
A simpler syntax might be
pushd %root%