So your still telling me that old Honda batter they used in the 90s maybe even still today I haven't been in parts biz in almost 20 years. But it was like 1.5 times the size of a lawnmower battery. Your telling me that little battery has as much stored power as a group 27 battery? I agree if engineered for higher cranking amps it could have them but no way it could produce them very long in that tiny case with such small amount of lead.
I am not one saying that we need 900cca for these small tractors just cause you can buy a better that produces it. These are small engines and not giant displacement engines that need much. Any size automotive battery will start them.
Well, I basically agree with Clemson....although Coy does have a point in a way - although the extra amps aren't really a "factor of lead in the battery". All else being equal, those extra amps are actually a function of how much Surface Area of that lead is exposed to the acid. Most batteries usea setup of parallel plates, so bigger and heavier means more surface area and hence more amps no matter how you measure them. But not always....
Not always, because that surface area can be increased in several other ways. One common way is by using some form of tricky lead plate geometry. Optima batteries do this by winding the lead into a cylinder instead of using parallel plates. Others do it with a waffle-like surface pattern on the plates. Both are more money. I appreciate the effort & don't mind paying the price $$ sometimes, but their sophisticated plate shape does make it an expensive battery.
And it's not just the extra price for the nifty plate shape, the problem is even worse because even for twice the price I don't actually get much of a reduction in battery size & weight - there's a little benefit; but not a whole lot.
In general it's just as Clemson says, heavier and larger batteries have more of every kind of useful power - how could they not? But also as he says, even a small automotive battery will spin one of our compact tractors well enough to start it in the worst weather. That's all you need.
Case in point: Our old YM165 Yanmar came from the factory with some sort of physically small, cheap, & lightweight garden tractor battery. You've seen the kind - sort of a clear greenish plastic case and a type common to motorcycles and lawnmowers. That battery was marginal in the best of weather even when new. Just not enough amps.... So I replaced it with a small automotive battery and it would spin that little diesel up at any temp.
IMHO, the best advice here is to figure out how to mount a small automotive group 24 or 27 auto battery in your Yanmar. It makes a world of difference and is all you need. A sealed type battery will keep the terminals cleaner and make the cables last longer. So get that kind if you can.
rScotty