I just saw a link to a very helpful site on batteries in a thread below but
now I can't find the OP. Thanks to whoever posted it.

I particularly recommend this page:

http://jgdarden.com/batteryfaq/carfaq1.htm

Note the number of times he says "or use AGM batteries" after describing
something you must do with safety glasses and other gear.

Note especially item number 1.13 where he says:

1.13. Do NOT use wet lead-acid batteries around salt water. If salt water is
mixed with the battery's electrolyte, deadly chlorine gas is produced. Only
use sealed AGM (Ca/Ca) or Gel Cell (Ca/Ca) VRLA batteries around salt water.

Good advice I think.

--
Roger Long