I would never take that pack on a train (or any other closed transport). That would be criminal, but then again, I think that that's the case for all e-bikes. I've seen way too many videos of packs going up without a warning and there is a ton of really bad advice out there from well meaning individuals who have absolutely no idea what they are doing.

The welds on this pack are very good, I have checked and re-checked all of them, inspected the pack using a FLIR while running at maximum charge / discharge just to make sure there is no hidden jump in resistance or a bad cell. The whole thing is wrapped in shock absorbent foam but it still is a massive pack and if it were to go into thermal runaway there is just too much energy there to be dealt with.

It stays outside and is charged outside and I'm monitoring the cells groups to mV precision to make sure that they're not misbehaving. I'm not taking any risks with 170 charged 18650s, if I would so much as drop or bump the bike I would discharge the pack and dismantle it.

I'd be worried about getting into a crash on this bike. (still an awesome project)