Hi Dennis "Doc" the creator of the Bionic Dolphin has sold me on Optima AGM batteries. He has had them down to 150 feet, completely exposed to the pressure. He only sealed the terminals with "E6000" urethane sealant available at Ace Hardware. He recently retired one of these batteries after 9 years of service. I am planing on 7 of them. Doug Jackson www.jackson.parcabul.com/sub