This project is a good reminder I really should finish that LiIon article that I've had on the back burner ever since I built the long range e-bike.<p>Some observations just from the pictures:<p>- corners of the nickel strips are not rounded, chances of cutting through the insulation of the cells, and in the high res pictures you can see some places where that might already be happening.<p>- welds are all over the place, from nice penetration to very shallow, possibly welds with high resistance, possibly burn through of the interconnects.<p>- physical construction of the pack is dangerous, no protection against impact if the whole construct is dropped. If it ever is dropped I would recommend immediately placing it in a fireproof container that is not indoors. And don't transport it in elevators or vehicles.<p>- no insulation rings between the tops of the batteries and the metal strips! That's really asking for trouble. You can see more than one spot on the pictures where the metal strip is directly in contact with the plastic and the welding process has likely further reduced the safety margin. The plastic sheathing of the cells is not enough protection for this kind of construction. Any insulation failure there means that you now have shorted an unfused pod and that pretty much guarantees a fire.<p>- balancing wires cross and pass over parts of the pack at a different voltage, a short of a balance wire can set off a thermal runaway.<p>- in general, wire management needs to be substantially improved if this is ever to become safe. Way too many wires that carry wildly different voltages cross and recross, especially close to soldering joints that might cause issues because the wires tend to shift inside the insulation if they're under tension while soldering.<p>I'm both impressed and horrified, this is the most clear illustration ever that I've seen for 'knows enough to be dangerous'. Laying out the sense/balance wires on a pack is a lot of work if you want to do it safely and even the pros (looking at you, Bosch) get this wrong. The result is that if ever one of the sense wires shorts out that it will essentially become a fuse and the energy imparted to the cells may just be enough to set off a thermal runaway. Wire management on the project here is terrible.