This is a parametric battery case, for usage with generic AA and AAA batteries. 

It uses as inspiration the battery cases I have seen here, but I did not like the fact that you were unable to easily change number of batteries or type of battery or in some cases you needed thin metal plates to act as the contact between the battery and the wire.

With this model, you can simply use metal wires (not included) (I used 0.5 mm gauge), be it single wire or thinner multi wires. Simply thread the wire through the holes. For the spring end, I recommend using a small, 2mm washer (not included - optional) to attach to your wire and act as a stopper, or simply add a thicker bead of solder (not included) to the wire to act as a stopper. On the non-spring end, you simply run one end of your wire and loop it a couple of times over the top edge (see pictures). How you wire up your batteries (series or paralllel) is up to you, though the model facilitates the series approach.

It uses the spring code from “Parametric Bobblehead Springs” by 3D Printy under the Creative Commons - Attribution license to which I've removed the parametric functionality of the spring, changed the spring coils to be further apart to ensure more travel, as well as removal of the end caps.