Those batch files work fine if I double-click them or run them from command line. However, after adding them as tasks to run in Task Scheduler, they never run no matter I manually click the Run button or set them to run at a scheduled time.

After searching on Internet, I found the reason:

When setting up task for the batch file, I selected “Run whether user is logged on or not” in Security options. As said in Task Scheduler help document, “If this radio button is selected, tasks will not run interactively. To make a task run interactively, select the Run only when user is logged on radio button.”
That means the tasks do run in my case, while they’re running in background without any UI that users can interact.

After changing the option to “Run only when user is logged on”, the command window pops up and my batch file runs as expected.

The answer was found from http://social.technet.microsoft.com/Forums/en/w7itprogeneral/thread/c03d6691-b058-4f8d-961c-e8eba25bbaed.