> I saw nothing about shock and vibration design, no drop tests, no mention of short circuit tests, no thermal measurements taken during a controlled charge/discharge, no mention of arc flash considerations during your assembly
So, this is why this project took a couple of months instead of a few days. I don't just slap stuff together.
The pack is 9 layers, has two inner layers of foam to cushion shocks, is shrink wrapped twice, uses high density ABS spacers instead of glue the way other people build their packs (at the expense of some space), has the wiring very carefully routed so that shorts are not just unlikely but pretty much impossible. The 'inconsistent' welds problem was solved by the overkill method: where a manufacturer would use two welds I used six, trial welds on bad cells proved that I could not tear the cells from the welds without major damage to the cell structure, in other words: those welds are pretty solid. I also measured their internal resistance across all cell groups, and monitored each group during a pretty stressful charge/discharge cycle to see what would happen to the interconnects. On the electrical front there is thermal monitoring, voltage and current monitoring, short circuit protection, overcharge and undercharge protection.
That pack is safe, short of getting crushed.
Also, and in case you're not a aware of it, I built a one-off windmill, 5 meters in diameter, rated for 2.5 KW, had a couple of Canadian winter storms attempt to take it down but it survived everything, built an overhead crane, a computer controlled plasma cutter and owned a fair sized machine shop. I'm not your average DIY person, and spent probably more time on safety on this particular design than I did on anything else.
I would trust this pack over a manufactured one, including the ones that Bosch puts out. I didn't do a drop test but that's mostly because this is a one-off and a after a drop test I would simply discard the pack, there is no way to do that non-destructively with a battery this heavy. That said, I'm very sure that the pack inside the foam core would be fine (it's dimensioned for that) but the housing would crack for sure.
As for why the bike is still legal: type approval is mostly related to the drive train, the maximum power the motor can put out, the degree to which it amplifies the pedal input power and various cut-outs, the batteries are not subject to the type approval, you can buy and fit aftermarket batteries for many bikes.
That said, your concern is appreciated.