I need to purchase a new battery for my 9.9 HP outboard.  What is the suggested MCA/CCA for a 2 stroke, 9.9 HP outboard?  I can't find any support on the web and I don't have an owner's manual.  The motor is a 1988 Evinrude 9.9 HP tiller.

Thanks for the help,

A lawn mower or motorcycle battery will start that little motor. I would base the battery size on how much other stuff it has to power, like a sonar, livewell pump, navigation lights, etc.

A group 24 marine starting battery should be plenty.

Don't get a starting battery, go for a deep cycle battery if you can find one that is small enough.  Deep cycle batteries will have more than sufficient amps to start that motor and they will give you better support for instruments, accessories etc.