[Svartalfiar]

Sodium reacts violently with water.
More water will just make it worse.
Wonder how a smashed open sodium battery will react to a fire hose.

And yet all table salt (sodium chloride) does with water is dissolve in it.

Are these batteries using pure sodium (highly doubtful)? Flammability and reactivity can vary greatly depending on what other stuff the batteries are made out of. They may be completely inert, or just as explosive as you think. I didn't see much clarification on that.

[BitWielder1]

Because the sodium already reacted with chlorine.
They did not say sodium chlorine batteries.
Even though you can do that. Any two different metals in salt water makes a small battery. Played with that as a kid. Mom would not let me use sulfuric acid.

It's funny how two elements so highly reactive and toxic makes something essential for life as we know it.