The CAD files can be downloaded from the autodesk fusion360 site and printed. Probably in the next few weeks we'll include battery holders in the bottom part of the build. Current build includes these found on thingyverse (link and mention will be added soon).

The battery's were added 3 parallel packs of 3 in series. Wired together with some scrapped cabling from an old PC power supply.

There really is no special secret to this, the entire project was  put together in a really short time frame and just for fun.

If you really want to build this, I would suggest including at least some circuitry to protect the cells from discharching too much and probably also added to the monitoring part, a charging circuit.