Here is my situation. We are home for the winter in IL and the boat is winterized in her slip in TN. Our slip neighbors noticed the smoke alarm going off and when they went over to investigate noticed a sulphur smell. They checked the 8d batteries and found that the water had cooked out of the SB battery. Apparently, the port battery was ok. I had topped off the batteries with water when we winterized it in Dec. The only AC load turned on was the battery charger in case it needed to charge the batteries if the bilge pumps went off. There should not be any constant DC loads turned on. My first question is why would the smoke alarm go off in the salon? The batteries are in the aft lazarette. I should be able to test the cells in the battery to see if it is bad, but was wondering how I can test the 3 Stage Battery charger to make sure it is working properly. I'm not sure why it would cook the battery if no DC loads were applied and why this happened if supposedly the charger should have been in the float mode? To be safe I had the neighbor cut the power at the shore power pedestal so just hope the boat doesn't start sinking. Hope to get down to the boat next month. Thanks for any insights and your recommendations!!!