While all JuiceBox kits and assembled units now ship fully pre-programmed with the latest software, this is an open source project, right? So you would like to tweak the firmware, change the parameters your display shows, etc, etc. For this, you will need a programming cable that attaches to a programming header on your JuiceBox (see the assembly manual at http://emotorwerks.com/JuiceBox_Public/ for your version). This programming cable is called FTDI cable.
Our pricing on this is lower than SparkFun's pricing, guaranteed.