4S1P High Power (weldless/experimental)

!!!IMPORTANT!!! Battery pack is one of its kind and completely experimental. Do this at you own risk!!! Wouldn't recommend building it as a first pack. Never leave live wires unprotected. Protect them before final assembly of the pack.

Perfect for high power or bass heavy portable speakers !!!  

 What I used for the pack:
Copper strip 6mm wide and 1.5mm thick. It was salvaged from old transformer or something. 
8 pcs Nickel plated springs. 7.5mm outside diameter, 5mm inner diameter, 20mm height, made of 1.2mm wire. (see picture).
15awg/18awg silicone tinned copper wires.
4S40A BMS from China.
12pcs m3-30 screws.
12pcs heat inserts.
Everything else is printed.

I would like to do deep testing, but I have nothing that I could run on it, only the amplifier. So my testing so far was very basic:

A 4-hour continuous stress test at 50% volume on the bench only dropped the pack from 16.34V to 16.03V (0.31V total), with essentially zero rebound after turning it off—perfectly proving the extreme low resistance and efficiency of the spring-loaded copper busbars. (30W + 30W Dayton Audio pc83-4 + 4inch passives)

BMS drains only 0.01V or less in 3 days. 

Even when battery is at 1% of charge, the pack still delivers great performance.

Voltage sag that I've seen so far during max volume was only 0.07V. (At 50% volume it fills up indoor basketball court with music nicely with basically non-existent 0.01-0.04V sag)

When starting voltage was 16.5V I listened to some music at 30-40% volume for 1 hour. Pack discharged only 0.1V. (That was actually surprising.)

I tried shaking it while the music was playing, and everything was alright. Nothing moves inside the battery pack sarcophagus. (But the cells still can expand and contract during charge and discharge in all directions)

All these indicate so far that the pack is healthy and should be low resistance. I used Ampace jp40's.

I uploaded my hand drawn sketch (I sketched it for myself so no judgment :D) for the copper strips and cell orientation, but in short you need:
3pcs - 6 x 33mm copper
10pcs - 6 x 10mm copper
Need to solder them as you see in picture. Then pre-tin all contact surfaces that will be touching the cells, and then file them flat. (I filed too much, but it is what it is). I will dismantle the pack after a few months to see if there's any corrosion). Solder wires to the copper busbars. Wires on small busbars of positive and negative terminals need to be soldered in a way so when you put the spring on, nothing tilts and everything stays flat(just file around until you get the shape you need). Assemble everything without the cells first, to see if screw holes align properly. After everything is assembled, I recommend to tape the pack so it would relieve the stress on the screws and heat inserts. 

Printed in PETG.
4walls.
20% infill.

Some updates may come in the future.