It's EXTREMELY simple to use the Mac Automator programme for this.

1. Create a workflow folder action: choose 'Actions' then 'Files and folders'. Choose 'Ask for finder items' and specify a folder into which you should drag the files to be processed.
2. Choose 'Actions' then 'Files and folders' and add 'Copy finder items' to the workflow. Specify a folder where your results should appear.
3. Add 'Rename finder items' to the workflow. Specify 'Change case' of 'Full name' to 'lower case'. Save the workflow. Now simply drag or copy your files into the first folder and they will be renamed all lower case into the second folder.