I didn’t think you were supposed to use a deep cycle battery as your starter battery. Just for the “house” battery on boats with a separate battery to power accessories when the engine is off. I thought I read that deep cycle batteries will have a shorter life when used that way (cranking). I’m NOT an expert so my advise is worth what you paid for it...
http://www.crownbattery.com/news/cra...marine-battery