Turbostart/Axion came out with a really good Sealed Delco Top Post R-59 just this past summer,that has a Sears DieHard like guts,meaning it's not a smaller downscaled ATV battery inside,but rather solid gel cells just like todays car batteries.It weighs roughly 50 lbs. and is completely maintenance free with a dead on look of the original R-59.
I bought two this summer and they both perform flawlessly with a 4 year warranty.They can crank forever if need be,rated at 650 cca.
I paid $150 for each battery before shipping,as they do discount on some volume orders.
SR-59 Battery (The script comes in red,not yellow as the pic shows.)