Or if an unrelated fire occurs in the garage/basement where it's located...
This is certainly enough stored energy to seriously ruin a firefighter's day if they didn't know it was there and how to properly deal with (or, more properly, to not bother dealing with it until it burns out).
That, to my untrained eye, looks like enough batteries to take down nearby structures if they went up, and packaged in such a way that a runaway in one cell that caused it to vent would propagate to other cells nearby.
Granted they're pretty reasonably protected by 2-3 layers of electronic monitoring and on-cell fuses, but lord, a small fire would burn the neighborhood.
I think all that it would take to render them marginally safer is a firewall between the different packs made of some good steel or refractory material.
> Even new pouch cells are way safer than they used to be.
Right, because these packs filled with recycled cells are going to have the latest protections.
> Unregulated 18650 cells are quite safe if the correct circuitry is used.
Which is my whole point, I'm not sure I trust the guy down the street to correctly wire and have adequate circuit protection for his DIY battery pack in his garage.
> The only dependable way to ignite them is to smash completely open them at full charge.
But there's no explosion risk unless there's something very wrong with the way they're packaged.