Good marine cranking batteries include the Dual PRO LS 3100 AGM battery, Optima batteries 8027-127-FFP D27M and the Duracell AGM Deep Cycle Marine and RV battery -- Group size 31. These batteries have all received high ratings or reviews.
Robert Hamilton of Bassfan.com claims the Dual PRO LS 3100 AGM battery is the best marine cranking battery on the market due to its power, capacity and reliability.
Users at Amazon.com give the Optima batteries 8027-127-FFP D27M four and a half stars overall. The company says the battery is designed to have a longer life span and greater vibration resistance than other batteries.
Sam's Club users give the Duracell AGM Deep Cycle Marine and RV battery five stars. It is specially designed for long, deep marine discharges and for starting motors.