My powersupply does not go below 5V, nor is it happy with current above 4A. I was tired of using crappy battery boxes, with crappy wires, and connection points. Usually the boxes were too tight for my batteries, and when modded, they were still mediocre, at best…
So this evening, I made my own “box”. Its not well “engineered”, good looking or anything. But it gets the job done. 
Springs come from CNQ.
I used a cooking plate to easily solder the springs onto the copper plates. Added a thick wire that can come in handy…
Used a glue gun to attach the copper plates to the wood.
22 AWG vs some really thick wire I used…
I will probably attach one or two extra wires directly to the copper plates, and add a switch.
Maybe this inspires someone to make their own box, parallel or series (which is a bit more work). Could come in handy for those who does not have a power supply, or just if you want to simulate how batteries work together with a certain driver circuit.