Path Variable

How can I add a permanent path to the system path environment variable. If I add it by opening a command prompt or running a batch file using the PATH=%PATH%;*New Path Location* it only stores it temporarily in the user environment variable. I have tried the registry entry HKLM\System\CurrentControlSet\Control\Session Manager\Environment\Path which works but I cannot amend this registry setting via a batch file\command prompt as the DOS box complains that the line is too long.