I don't doubt they have all of those issues covered, but was looking at some of the damage reports from Hurricane Sandy on the subway in Manhattan and thought "hmm if a surge of saltwater submerged one of these things you would only have a limited time to get it un-submerged before the saltwater got into the packs. When that happened you'd be in a world of hurt.
There was some drama about a bunch of Fisker EVs catching fire[1] after immersion, but apparently[2] not (directly) battery-related.
Offhand, I'm not sure if the specific battery chemistry requires vents for in/out-gassing, or whether you could reasonably fully seal them. Or I suppose you could[3]
have the battery pack detect such a condition and use its power to electrolyse some water to keep the pack at positive pressure. Or maybe some kind of self-destruct that dumps the stored energy into a chemical reaction or passivates the cells somehow (wave hands)
