From experience - if you don't have 900 cranking amps available the computer on the Opti will not allow it to fire. As FrFrank said - it will turn over but not fire. You have to have a good cranking battery. And if you plan to anchor and fish offshore, make sure your cranking battery is isolated from your "other stuff" battery. Trust me - that other stuff will draw the battery down enough to prevent the Opti from firing. Been there, done that, been helped in.