Buy batteries by weight not CCA. Heavier=more lead=longer life and deeper discharge. Buy the heaviest battery that will fit the space. Group 27 marine deep cell in either flooded or AGM you can't go wrong. Odyssey, Deka, Trojan, and Surette/Rolls are the brands you should be shopping.
Engine starting batteries are like sprinters...Lots of energy for short bursts but not long winded. Deep cycle is like a marathon runner...pretty even discharge for long periods. The stating batteries have plates with open mesh for a lot of surface area so that there can be a lot of electrons flowing when needed. Deep cycle the plates are almost solid so that the discharge is slower.
You can certainly use a deep cell for engine starting but you shouldn't use a start battery for long periods.
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1994 RRC LeWiB "ruining the air behind me"
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