This design is derived from the parameterized Battery compartment: thingiverse.com/thing:5051 (By Guru). I have added a simple method for the electrical connections. The proof of concept was tested on this thing: thingiverse.com/thing:5070NOW you can print your own fully-functional battery pack :-)For every battery there are two embedded nuts in contact with the positive and negative poles. Two metal M3 bolts are inserted from the outside. They will contact with the poles. Now, you have a wonderful electrical access to the battery!!I have tested with 2-AAA and 4-AAA battery packs. It worked like a charm :-)In addition, I have added more parameters for generating the battery pack: the thickness of the bottom, front and rear, and side walls as well as the distance between two batteries.Update: Jan/30/2011. Added the contribution of eaglepex ( http://www.thingiverse.com/eagleapex ). Now the batteries can also be in serial connection changing the ser parameter(1) There is a simple and powerful trick to embed the nuts into their slots (as shown in the pictures). Insert a M3 12mm bolt with a washer form the outside. Add the nut in the inside part. Screw the bolt until the nut reach the socket. Now, put the nut in the correct orientation so that it can enter the socket. Screw the bolts until the nut fits perfectly. Then remove the bolt. The nut will remain in its socket.(2) WARNING: The batteries can be inserted with different orientations. Make sure they are inserted with alternating poles: +, -, +, - so that they can be connected in serial.(3) Once the bolts are put, it is time to set the electrical connections. Connect the batteries in serial (Be careful of the short cuts!). It can be used standard wires. Or alternatively you can use Clips, as shown in the pictures.Instruction for building a 2-battery-pack See the following images: http://fotos.iearobotics.com/index.php?album=objetos-3dââ??â??=dsc01654.jpg ("Sig" means Next, "Ant" means Prev)Instruction for building a 4-battery-pack See the following images: http://fotos.iearobotics.com/index.php?album=objetos-3dââ??â??=dsc01674.jpg ("Sig" means Next, "Ant" means Prev)