How to NOT wait for a process to complete in batch script?

Why not just start somecmd.exe or start "" "some command with spaces.exe"?

Note that if your command has spaces, you must put quotes around it, but if the first argument to start has quote around it the command is the second argument, so I have two sets of quotes there.

Use

START c:\wherever\whatever.exe

This will probably suffice.

call "cmd /c start notepad.exe"