... and how many USB charged batteries have you seen explode to the point of engulfing that much of a structure?
While what I witnessed wasn't on a boat, I have seen the results of a camera and light batteries catching on fire during the night while charging.
In Nov of 2018, I was in Philippines at a dive resort.
The dive house had a handful of camera stations in a common area.
One morning I came out to the dive house and noticed that there had been a fire the night before at one of the camera stations.
The camera housing, the twin lights and arms were all a black melted mess of charred remains along with lots of black charring in the nearby surrounding area.
Luckily in this case, the table/shelf for the camera stations was made of concrete and the wall behind it was concrete cinder block. So while there was a lot of charring on the table and black residue on the wall up to the ceiling, along with lots of melted stuff in that station area, and the person lost their camera setup, the building did not catch on fire.
I'm not saying that a battery issue is what caused caused the fire on the boat, but that these types of battery issues do happen, and when they do, they generate immense heat and have the potential to cause the surrounding materials to light on fire from the flames and the intense heat generated.
--- bill