About the danger of sodium violent reaction in case get contact with water, I believe it refer to sodium hydroxide (NaOH) , and not the typical sodium chloride NaCL (cooking salt).
Well, a good question would be about what kind of sodium they will use. But I believe it's hydroxide. Anyway the cells are closed, each unit, and also a final cover to encapsulate a bunch of cells. So the risk of contact with water would be very low.