%date:~10,4%_%date:~7,2%_%date:~4,2%_%time:~0,2%%time:~3,2%
output:
2013_06_13_2004 (year_month_day)
source: http://www.tech-recipes.com/rx/956/windows-batch-file-bat-to-get-current-date-in-mmddyyyy-format/