This is the RDLogics Starter Box II for the Traxxas Revo 2.5 and 3.3 trucks.  This features a new, wider belt design for longer life and more torque to start your engine.  This runs off two 7.2V stick packs, or a 12V battery or power source.  Batteries are not included, but are available.  Your truck must have a flywheel large enough for use with a starter box.  If you need a flywheel, get the Traxxas TRA4142X.