Sea water and lead acid batteries = Chlorine Gas which is a problem in an airtight vessel 1200 feet below the surface while trying to be silent .
Last batteries I seen for that application were 2.2volts each and about the size of a 30 gallon barrel but square instead of round. Heavy copper buss bar is bolted between lug to lug to series the bank up to a nominal voltage of 250V. The current capacity is so high that each battery has two negative terminals and two positive terminals. Ventilation of the hydrogen , oxygen and SO2 fumes methods vary with the application. Sometimes a demineralized water addition system is also plumbed in.
