New Moto Guzzi Door Mats Available Now
OK it was this one---------- bought 2 of them, price went up a bithttps://www.batteriesplus.com/productdetails/battery/ups/sladc12=35j
If you're going to use a garden tractor battery, please spend the few extra $$ for a sealed one instead one that vents out the caps on top.
That link you supplied is for a deep cycle battery. Deep cycle's are different than your standard lead acid battery used for starting a car/motor sports vehicle. I'm not saying it won't work (kinda hard to do that in the face of contrary evidence) but it is not the best option for the application.
Changing the starter from the Bosch original to the Valeo latter unit will allow the use of a much smaller battery (less cca) and more options for the battery.