The same extension as all the other scripts. Why not create the file Put a file in C:\Windows\temp and try the script to see if it it works.
It would be fast on the same disk if move would work all that would be done is the directory file entries would be moved. The File data will remain as is. However it look like to use move you would need to enumerate all the file names. Wild cards are not supported. You will need to use copy and del in order to use wild cards.
try{
var BAT = new File(Folder.temp + "/MoveFilesToArchive.bat");
BAT.open("w");
BAT.writeln('Copy /Y "c:\\windows\\temp\\*.jpg" "c:\\temp\\*.*"');
BAT.writeln('Del "c:\\windows\\temp\\*.jpg"');
BAT.close();
BAT.execute(); // execute the temp bat file
}catch(e){
alert("Bat MoveFilesToArchive failed to execute.");
};