How to run multiple SQL scripts using a batch file?

You can create a Strored Procedure to call all your Scripts. You could also create a schedule plan to run the scripts automaticaly.

http://msdn.microsoft.com/en-us/library/aa174792(v=sql.80).aspx

Yes, it's possible. You can do it with :r command of SQLCMD.

I strongly recommend you to read this article and do it with SQLCMD

http://www.mssqltips.com/sqlservertip/1543/using-sqlcmd-to-execute-multiple-sql-server-scripts/

You've got an unmatched parenthesis, there. Try

for %%f in (*.sql) do sqlcmd.exe -S servername -E -d databasename -i %%f >>output.txt

I just saved it in a .cmd file and it appears to be working.