This should start a good discussion, lots of things to consider; location of the batteries relative to the engine for Cold Cranking Amps, engine alternator size, accessory load, etc. Sounds you have a pretty good amp draw potential. There are a couple of camps in our forum as to which type of battery to use. My personal choice is group 29 or larger, 1000 CCA, min 150 minute reserve dual purpose cranking and deep cycle X 2 from Autozone, about $115 ea. with good maintenance expect a 4-5 year life. I run with my battery switch on "both". I am a firm believer in overkill on batteries. You may want to consider a third large deep cycle or dual purpose for your radar and electronics with a battery isolator. You should be getting a ton of advice by supper time tonight.