Originally Posted by MarkofSeaLife
Yes, but read the ops post
He is NOT going to deep cycle the batteries.
He is NLT sing them to start. He's taking a camping light. No refrigeration.
Where, tell me is there deep cycle in his elec usage?
Read his post.
And the flip side of that question is what advantage does the starting battery have?
If it has 6x the CCA requirement of the engine the answer is very little. Meanwhile those extra unused CCA's come at the expense of Ah's that can actually be used for lights and the radio. On top of that the design compromises that squeeze out the extra cranking amps severely reduce the lifetime of the battery when it's deep cycled.
Starting batteries are essentially tailored for cars which 1) Have giant engines for their size which need lots of CCA's and 2) run the engine 99% of the time they're used.
By contrast, sailboats go days between charges and have lights and radios which over a couple days of cruising can easily use up 20-40% of a smallish bank (especially if they're not LED). I just have a hard time seeing a use-case constructed where the starting battery is a better choice.