I bought the boat last year and the batteries at 7 years old were considering EOL. We negotiated further on battery replacement as part of the deal but I'm still hanging in there with my 4 T105's. I haven't taken specific gravity readings but they don't seem to be losing charge at all. I've kept them topped off over the winter and have a small Ganz 12 watt solar panel to trickle charge when at the mooring.

I expect to get at least this season out of them...hopefully more.