Holds 2 (two) 9 Volt Batteries, We wire them in parallel to power an Arduino UNO R3. This case is the power unit to our Buzz and Bark Box. The case itself can be stand alone or mounted. The (4) rectangular holes fit our mount feet pegs or used as a mount hole. If you're interested in getting one of these with the wiring harness you can visit us at http://www.badbrick.com/catalog In MakerWare, I modify the "Medium" settings: Quality: Layer Height = 0.2 and I increase the temp to 240C to let the little larger prints fuse better. All other defaults are the same. ** Please note to Maker Ware users. I've downgraded our MW back to 2.1.x and the firmware back to 7.1. For some reason our STLs were not printing correctly with the new 2.2 update. The slicer was printing partial faces that are not in the model. Just a heads up. You may totally different setup the we have.. So.. Just to know.