could not locate my own executable path

I tried to use a set of batch files to start postmaster under win32 for
a while and I had these errors when I tried to connect from psql.

<>LOG:  could not find a "postgres" to execute
FATAL:  postgres: could not locate my own executable path


I was able to correct it by (in the batch file) changing the working
directory to the install directory of postgresql.   Is postmaster gets
its working directory from the environment and not the path name of the
exectuble?