Have you ever wondered why a 100HP outboard requires a 800CCA battery? It actually has nothing to do with 800 cold cranking amps and the 30 second discharge time at minus 18 deg centigrade.

A 100HP outboard these days has an electronic ignition system and a high torque starter motor which only draws about 150-200A. It will start in 1 second so you could actually use a 7Ah alarm battery you use on your fish finder to start the outboard. It might, however, record a low voltage warning in the engine management ECU, and that if done repeatedly will void your mechanical warranty of the outboard. The low voltage happens when you draw high current from a small capacity battery, the voltage dips but when the discharge turns off the voltage goes back up.

So this is why you are told 800CCA. A few things to note also, have you ever noticed that there are plenty of batteries just under the magic 800CCA that are $80-100 less? That's because back in the day the outboard manufacturer being local to a country had to determine what was locally available and suitable. Many times that lead to supply agreements and those agreements were made to benefit one brand over all the others with not quite enough CCA. Anyway I digress, the reason for 800CCA is that a typical battery would have to be approx 80-90Ah to achieve that kind of spec and if its 80 plus Amp Hour then even if the battery is a few years old and is half discharged, you've got some electronics on prior to turning the key and the temp is a chilly few degrees above freezing. The battery will still have enough power to start your outboard.

There you have it, a worst-case scenario used to resolve a starting point and avoid liability of being sued. (a genuine concern if you are in America)