RR .... see if any of this helps : http://www.batteriesinaflash.com/deep-cycle-battery-faq (most especially the section titled "What are the differences between a starting and deep cycle battery?"

Not really much help in this dept., as I've only had ONE battery (Marine Deep Cycle) running everything .. on my first two boats, and my buddy's boat (that I fished out of when not having my own boat). The boat I have now is the first boat I've owned that has two batteries ... one starting (G24) & one TM (G27). Boat/motor are 1999 model (motor is 90hp Merc). Console DF is hooked to starting battery ... bow DF is hooked into TM wiring. No interference experienced. Starting battery rarely needs a recharge, as 90Merc seems to replace any charge removed for starting.

I'll get back to you on the specs of the starting battery. But, I'd go with whatever CatFan says !!

... cp