You'll just get less capacity if BMS was wired to monitor individual cells and reported capacity based on that. If you were just measuring voltages at the bus bar, you could over-drain or otherwise over-strain the outlier cell and set it on fire.

Which don't happen often enough to make Amazon do something about fake packs for drills and Dyson vacuums, but I think the chance increases as cell count increases and idiot-proofness decreases.

The replacement process would be almost the same.

Well, article title implies single battery (and not parts of it being replaced regularly) that lasts lifetime. With current technology the only way to achieve that it it to make it explode rather violently. In all seriousness, the issue with that battery's approach is only if it can fit any specific bike, otherwise idea is good since 18650 batteries are highy standardized. except new chemistry right around corner, and new chemistry means different voltages etc

It's also explicitly listed in their documentation: https://docs.gouach.com/knowledge-base/frequently-asked-ques...