220 CCA battery at a minimum. Li-Ions are rated much higher but they cheat the test a bit... The Battery Rule is: You get that you pay for.
I'll check what a healthy stock Buell starter draws with my induction ammeter when I get home, it's a good question and I'd like to know myself. But if you're asking which of the aftermarket ones to pick... pay for the BIG one and be SURE its the right one. The Sportster version will bolt-on but has the wrong nose cone and will let oil out of the primary at higher RPM's.
I'll check what a healthy stock Buell starter draws with my induction ammeter when I get home, it's a good question and I'd like to know myself. But if you're asking which of the aftermarket ones to pick... pay for the BIG one and be SURE its the right one. The Sportster version will bolt-on but has the wrong nose cone and will let oil out of the primary at higher RPM's.