This is what has worked for me. I use this to "add" files over to the other drive, with no overwrites.
Batch file: robocopy-missingfiles.bat
@echo off
echo Copying
echo "%1"
echo to "%2"
echo.
echo Press Cntr+C to abort
Pause
echo.
@echo on
robocopy %1 %2 /Xo /XN /XC /J /SL /S /MT:8 /R:1 /W:1 /V /DCOPY:DAT /ETA /COPY:DATO /FFT /A-:SH /XD $RECYCLE.BIN "System Volume Information"
Example:
robocopy-missingfiles.bat f:\Working-folder\ E:\Backup-folder\
Do test before implementation.