Thanks for your responses for advice on sealed marine batteries. After further investigation, I decided to replace the two sealed liquid filled batteries that were located in an unvented area beneath the aft quarter berth on my h33.5 with two absorbed glass matt (AGM) batteries. The batteries are manufactured by OPTIMA and are available from DC Battery Specialists (www.dcbattery.com/)The batteries for my application are blue top, Group 27, combination starting and deep cycle. Cost is $150 ea These batteries are leak proof even if the case is cracked. Vapor emission is negligible. My understanding is that these are in wide use throughout the military for applications in unvented spaces and where vibration and sudden impact could cause the case to crack.