Thanks a lot! I googled a bit and found that
start /?
will bring you more options (which may be helpfull if something other than /max is needed):
Syntax
START "title" [/Dpath] [options] "command" [parameters]

Key:
title : Text for the CMD window title bar (required)
path : Starting directory
command : The command, batch file or executable program to run
parameters : The parameters passed to the command

Options:
/MIN : Minimized
/MAX : Maximized
/WAIT : Start application and wait for it to terminate
/LOW : Use IDLE priority class
/NORMAL : Use NORMAL priority class
/HIGH : Use HIGH priority class
/REALTIME : Use REALTIME priority class

/B : Start application without creating a new window. In this case
^C will be ignored - leaving ^Break as the only way to
interrupt the application
/I : Ignore any changes to the current environment.

Options for 16-bit WINDOWS programs only

/SEPARATE Start in separate memory space (more robust)
/SHARED Start in shared memory space (default)

Also, ALT+ENTER should make it full screen.