Detect sqlplus error in dos batch script?

We have the following batch script:

(
echo @release.sql
echo exit
) | sqlplus x/y@orcl

if %errorlevel% gtr 1 goto dberror

Issue is - the statement if %errorlevel% gtr 1 never appears to be true when there is a sql error.

If we put garbage commands in the release.sql file, sqlplus does complain:

SQL> SP2-0042: unknown command "blah" - rest of line ignored.
SQL> Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production

But %errorlevel% still equals 0. How can we determine that there was a sql error?

Update: This code DOES appear to work for some sql errors. It will work if I do drop table blah but it won't work with just the command blah