In a soliloquy on batteries for electric vehicles, including ships, he pondered what would happen if such a boat were to sink and the battery would submerge.
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“It must be because of MIT, my relationship with MIT, very smart, I say, what would happen if the boat sank from its weight, and you have this tremendously powerful battery, and the battery is now underwater and there’s a shark that’s approximately 10 yards over there,” he said as MAGA supporters listened intently. “By the way, a lot of shark attacks lately. Did you notice this? A lot of sha…”
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“So there is a shark 10 yards from the boat, ten yards… or here,” he said. “Do I get electrocuted if the boat is sinking, water goes over the battery, the boat is sinking? Do I stay on top of the boat and get electrocuted, or do I jump over by the shark and not get electrocuted?”
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“He didn’t know. He said: ‘Nobody has ever asked me that question.’ I said, ‘I think it’s a good question. I think there is a lot of electric current coming through that water,’” Trump said. “But you know what I would do if there is a shark or you get electrocuted? I’ll take electrocution every single time.* I’m not getting near the shark.”
I don’t think they’ll burn under water. The main reason battery fires are hard to extinguish is because at high temperatures, metal oxides in them decompose and release oxygen gas. So you can’t extinguish the fire, but you can try to cool it down.
This deck on the NASA website illustrates that very little oxygen is released from a single cell
Per this video:
Submersing it in the ocean would probably cool it very quickly and put it out.