I think part of the problem is that you think I am saying "LFP batteries are dangerous." But what I am really saying is that under the right circumstances, LFP batteries can be ignited.So let me get this correct - LFP can be dangerous if put on a hot plate, or in the oven, or metal spikes drove through them, or they sit immersed in seawater for a year until they corrode (only the metal cased ones, though), and that a single incident in someone's mother's basement of a LFP battery "spontaneously" catching fire that has no other information, including the actual cause of the almost fire shows how this could be a bad thing on a boat.
You have totally convinced me of the dangers of LFP.
LFP batteries are safe enough for me.
But it would not take a year for cells inside a battery to corrode in seawater. Probably less than an hour. This is not passive corrosion I am talking about. It is electrolysis driven by the potential of the battery cells themselves. When you put two metal electrodes in seawater and there is enough potential between them, redox reactions occur at both electrodes. One of them will have junk stick to it and the other one will rapidly erode. Kind of like electroplating in reverse.
Battleborn batteries are plastic cased, but the actual cells inside (according to teardown videos) are cylindrical metal cells. Battleborn's website specifically says that in case of immersion or continual high humidity, moisture may enter the case and cause damage (no mention of fire, though). They do offer a waterproof kit which should probably be considered essential for mariners using Battleborn batteries, just for reliability, not necessarily for fire.
Other batteries use those monolithic, blue-wrapped cells. Or old-school CALB cells (not sure the details of construction on those but they look pretty robust). I don't know if the metal under the blue wrap is connected to either electrode of the battery. I could check that though because I have some 176 Ah blue-wrapped brick cells.
I understand your skepticism about the fire because there are so few details available. But the issue here is that skepticism must be applied most energetically to the things you want to believe. "The first principle is that you must not fool yourself, and you are the easiest person to fool." I have made my living designing electronics and occasionally I have screwed up and had things go wrong and I have had to figure out my mistake. What happens is someone says, hey, we have a widget that doesn't work. The QA tester said the flux capacitor caught on fire and now it doesn't work. You say that is impossible, the flux capacitor can't catch on fire. Its probably a fluke. If you leave it at that, then when production starts, you may very well find out that 1 out of 1000 units has a flux capacitor that catches on fire and you will have to stop production and figure out what is going on and fix it. The CEO will be getting daily briefings from your boss. It is uncomfortable.
The one LFP fire I know of is like the report of the flux capacitor. Much as I don't want to believe that LFP batteries can contribute to a fire on a boat, I now have a question in my mind about it. And YOU SHOULD TOO. This is not the same as saying that LFP batteries are unsafe. It is just about taking things seriously. It is frustrating to know so little about the failure though.
Being skeptical of things you don't want to believe is no special skill and is not a sign of a great scientific mind. In fact, a lot of people who invoke skepticism actually are idiots, and do it VERY selectively. It is simple human nature and is quite easy to do. Being skeptical of things you have become emotionally invested in is difficult but necessary. We make excuses for the ideas we love. I do try to avoid the emotional investment part, though, but I am not always successful.
I try to approach reports of failure with an open mind.