Recently I have had 2 cases in my life where family and friend have been left stranded due to dead batteries. In both case both batteries were maintenance free. Both batteries were just 24 months old. I checked the water level in each battery and found they both needed roughly 16 oz of water. I charged them up over night and now both are great. These 2 incidents happened about 3 weeks apart. I checked my 2 batteries in my boat last night and had to add about 5 oz to each of the maintenace free batteries. So what I am saying here is we should check the fluid level in our batteries as part of the maintenane process even if they are maintenace free. I don't want to see anybody get stranded because there was not enough water in the battery to keep it at full cranking amps.
These batteries in the cars were labeled maintenace free. Not quite sure about my boat batteries, they are Interstate RV/Marine. I thought as you both thougth that maintenance free batteries were sealed. But these were not.