I assumed they would use sea water for cooling but that doesn't seem to be the case? Maybe the battery coolant is cooled using some sort of sea water heat exchanger?
You really don't want to cool anything with sea water directly. It's corrosive due to the salt and contains all kinds of fun things from flotsam to critters, some of which might make a home in your cooling loop. in this case, additionally, sea water is conductive and that's not acceptable in a battery.
However, feeding the coolant through some sort of heat exchange with the sea water is very likely something they do.
However, feeding the coolant through some sort of heat exchange with the sea water is very likely something they do.