Its only a cheap diode placed in the battery circuit, so if you do cross polarise, it will protect the main important parts of the board and only blow a small 15 diode which takes 5mins to unsolder and replace. Saves you loosing $$$ because the diode wasnt there.

You can infact short circuit the diode afew times with out it blowing, weve had one person do it a few times and they still keep working.