Tex,
this is much like oil and grease and women's hair color ............ aint no real perfect answer, I prefer brunettes, does that help? Ok - kidding.
Measure the phyical size of your battery ..... LxHxW and note the terminal directions ..... some batteries DO switch the poles (most have a R behind the number series) - then go to where ever you wish to buy a battery, and get the largest CCA you can afford and place that in the tractor. And buy a "good" battery maintainer to boot. AND you should be happy for ........... 5-10 years! maybe.........