Marine/RV Starting/Deep Cycle Battery for engine starting

It depends on just how "deep cycle"" is the multipurpose battery, what is its output when temperature drops to -20 F, and how hard your engine is to crank and start when it is that cold.

I would have no problems being lightweight on cranking power in Florida, or anywhere on the West Coast where "cold" is just somewhere around freezing, but for winter in Montana or Alberta I would want a starting battery with the highest CCA that will fit in the battery box.