What Size Battery Do I need On My Yanmar Tractor?

Typically a Group 24 battery is what is used in most of the Yanmar YM series and F series tractors but the best way to get the correct battery for your tractor is to just take the old battery in to the parts store with you. They will be able to match it up there. You will have to take your old battery in anyway for a core exchange (or pay the core fee) so this is the easiest way to be sure you get the correct size & terminal type. The only thing you really need to 'match' is the overall physical size and the terminal position and style. You do not need to worry about matching CCA. 

If you don't have a battery to match then the best method is to just measure the size of the battery tray and match up a battery that way.

Getting a battery with a higher CCA will not hurt anything- they just generally cost more but they will give you more cranking power. Getting a battery with a very low CCA can make the starter turn the engine over slower and potentially hard to start. Typically any "car sized" battery will be more than enough to start your tractor. The only time you might get into trouble is if you buy one of the smaller 'garden tractor' or ATV size batteries. They might not have enough 'oomph' to start your tractor - especially in the cold. 

Don't be afraid to shop around. Battery prices can vary wildly even for the same exact battery with a different brand sticker on it. Walmart and Atwoods often has some very good battery prices.