The battery with the most Reserve Capacity I was able to find was a group 31 battery from VMAX. It has 265 Reserve Minutes (Which I did buy to use as a electronics battery). Was'nt cheap though, but I found nothing over 200 minutes in the same size. My Bluetop Optima I have as a cranking battery has only 120 minutes. Look at my post (Best Dual Purpose Battery) regarding that and it may answer some questions. Good luck.
P.S. VMAX was $349 shipped.
John 21:6
"Cast your net on the right side of the boat and you will find some." When they did they were unable to haul the net in because of the large number of fish.
Maybe we are just on the wrong side sometimes.....