When the battery died on my 850, I went to Auto Zone for another one. (If you're hung up on using all factory parts, move on) The battery size shown in the chart was group 47. I went to the battery rack, and there was a somewhat longer one there, a group 48, with more capacity for the same price. The alternator is big enough to handle it. I only had to do very minor re-routing of the negative cables to install it. There is even another notch in exactly the right place in the battery tray for the retainer to fit into to accommodate the longer battery.