I’ve just soldered my very first pack of 20 parallel 18650 cells. It doesn’t look beautiful, but it seems to work fine.

• cells are connected using 0.2 mm copper wire (~€0.10 per 1 m)
• busbars are made of 1 mm thick copper sheet, they are 10 mm wide (~€0.20 per bus bar)
• the pack uses two 4×5 plastic cell spacers bought on AliExpress (~€0.5 per spacer)
• the module consists of 20 cells between 700 - 1500 mAh each (it’s made of lower quality cells), I expect it to have around 20 Ah in total

A few thoughts so far:

• cutting busbars from a 1 mm copper sheet is easier than I initially thought - the cheapest cutters do the job well
• I need a little bit more powerful soldering iron to solder cells and busbars - especially the bottom side of a cell is a challenge
• I’ll try to make my cell spacers on my own (e.g. wooden ones)