Batch Mp3 Converter
The best tool to undertake the task at hand is the simpliest one that handles it
No-liability agreement:
Before downloading the program, however, you are warned that in order to execute it, you must accept its terms of use. Specifically, you are warned that this program is under continous development and that no claim is made regarding its suitability for any purpose.

In other words, it is stated here that in case anything goes wrong due to its execution, his programmer must not be considered liable for anything bad that might happen.
Downloads:
Below, you find the links to download the english version of the program.
batch-mp3-converter.exe (version 1.05) batch-mp3-converter.zip (version 1.05)