I have an Optima Blue Top AGM 31 I purchased back in August when out of town for a BFL and cranking battery failed, cost $350. This is what I used in my boat for trolling motor batteries but it doesn't have enough reserve AMP hours to use as a cranking battery with multiple depth finders. Only used it 3 days until failed battery was replaced my regular dealer. Just ordered new boat with lithiums so don't have a real reason to keep it. Sale for $175.