%date% depends on your computer settings, and locale. Here is a reliable way to get a date and time stamp. Win XP pro and above.
If you need to use your batch file on unknown machines then this is worth using.
:: time and date stamp YYYYMMDD, HHMMSS and YYYY-MM-DD_HH-MM-SS
@echo off
for /f "delims=" %%a in ('wmic OS Get localdatetime ^| find "."') do set dt=%%a
set datestamp=%dt:~0,8%
set timestamp=%dt:~8,6%
set YYYY=%dt:~0,4%
set MM=%dt:~4,2%
set DD=%dt:~6,2%
set HH=%dt:~8,2%
set Min=%dt:~10,2%
set Sec=%dt:~12,2%
set stamp=%YYYY%-%MM%-%DD%_%HH%-%Min%-%Sec%
echo stamp: "%stamp%"
echo datestamp: "%datestamp%"
echo timestamp: "%timestamp%"
pause