> I always wonder what happens when these things catch fire
If you're hoping someone will chime in to tell you they have magic firefighting foam inside them or something, I regret to inform you that what happens if it catches fire is exactly what one might naively expect from large lithium batteries.
Newer LiFePo4 (Lithium Iron Phosphate) batteries don't have the fire issues that the previous Lithium Ion generation did. They are a bit more expensive and heavier, but they are superior in every other way (safety, lifespan, max charge cycles).
If you're hoping someone will chime in to tell you they have magic firefighting foam inside them or something, I regret to inform you that what happens if it catches fire is exactly what one might naively expect from large lithium batteries.