Hello, i have a 1985 Wellcraft 248 sportsman. Has a GM 5.7 350 motor in it. Want to run 2 Battery but not sure on CCA for 2 battery's. I have a 800CCA for starting atm.
As to your original question about CCAs for a 2-battery set up, it more proper to think in terms of Amp Hrs (Ah) vs Cold Cranking Amps (CCA). Ah is the amount of energy the battery will put out. So, if running a device that draws 10 Amps a 100 Ah battery would theoretically run it for 10 hrs (Hrs = Ah/Amp or 10hrs = 100Ahr/10Amp).
CCA is all about starting an engine in cold weather, hence the name. Is CCA related to Ah? Well, yes. In general, a higher CCA means higher Ah. Here is a
link to understand the relationship between the two.
So back to your question: it really becomes one of why you are looking to do a 2-battery set up. Per posts 3 and 9, it seems you are looking to have a “house battery” that will be heavily loaded and desire 2 batteries to be confident you will be able to start after a long day of having fun.
Thus, the idea of using a “starting battery” for the engine and a “deep cycle battery” for the house loads is appropriate.
This can be accomplished a number of ways, including the aforenamed Blue Seas Add A Battey kit mentioned by Dingbat in post 11.
But there are considerations including the run time you spend vs. the having fun for the day.
So, as mentioned in post 22 by Dingbat, this is what it comes down to: figure out the house loads you plan on using (i.e. the total amps being pulled while your engine is shutdown) and for how long (this will give you Ah needed for the house battery) vs. the amount of time you will spend with the motor above idle, as in running out to your fun time spots (this will give you the approx. amount of Ah your alternator will put out using 60A x time). If unsure of the amp draw of a particular house item, look at the data plate or use the fuse size for it (i.e., if fuse if 5A assume it’s a full 5A draw, while it will not be, it’s a conservative value).
Post that that evaluation along with your backup data and folks will be able to guide you as to your best fit solution.