All good stuff in this thread. I still need to refine a few things but here’s the box so far. I had to reinforce the “cutting boards” as they were flexing a little. I also need different springs. The ones I used are supposedly rated to 190lbs or so but collapsed with 70lbs. I think I should also re-route the wires to avoid having them cross one another, seems unsafe.
But the box works nicely, the side plates move independently from the bottom as intended.
The box is made from Costco cutting boards, 1/8” aluminum, 5/16 rod, steel shelf mounts (those black bars, the 5/16 locknuts fit perfectly in the groove), 5/16 serrated nuts (the serration grabs the spring edge preventing the nut from backing off) and I used rubber appliance pads in between the cells and felt on the edges.
The last photo of this series shows the box before the 1/8" reinforcement, the added edges on the bottom plate and the positive 2AWG cable.