Which Battery is best?

[FishStretcher]

The biggest things to limit starting motor performance are the starter, cable connections, cable diameter, cable length, and the battery. If the battery is new, and fully charged regularly, then I think the type is mostly irrelevant. Certainly the outboard wasn't engineered to work with an AGM but not a flooded battery. And for recreational use, I think overcharging is far less likely than undercharging. And letting an undercharged battery sit is bad for life. There are only a few manufacturers but lots of brands. And generally capacity is related to the amount of lead and not a lot else. Starting power is related to plate surface area. Get the newest flooded battery you can- check the date code. And verify the cables and starter are in good shape. I have had more expensive batteries quit than Wal-Mart ones.