You can customize whether you want the batteries in parallel or series. It is reccomended you print the contact retainer at 0.10mm layer height (or use a smaller diameter nozzle). Here are the hardware I used for this model:

Battery contacts: 50pcs AAA Battery Positive-Negative Conversion Contact Spring Nickeling Plate 10x9mm

Screw terminals: 50pcs PCB Mount Screw Terminal Block Connectors 5mm Pitch (2P 30pcs,3P 10pcs,4Pin 10pcs)

You have to bend the pin on the terminal block. It should be a press fit