Got mine for the ST2 from fleabay, some cracking deals on there, undr half the price of a bike shop. Only problem buying by post is that you don't usually get the electrolyte in the battery so need to go to a tyre/battery place to get it filled.
I ain't to keen on the new "gel" batteries as once they get down on charge you can't bring them back like the old lead acid types. Got through a couple on the MV but fitted a non OEM part and seems fine now. Modern alarms drain the hell out of batteries over winter so I've a bunch of Optimates running on them all, seems to work fine.