Replacing Battery

[Bayou Sailor]

Hey Guys, I am going to replace Margarita's batteries soon. She has one start and one house. They are both automotive type 24's. I am going to replace them with AGM's. Of the two that I am looking at, one has 880CCA and one has 750CCA with about $120 price difference. I think 750 is plenty for an A4, but I wanted to double check with the professionals. What say you??? Thanks.

[edwardc]

More than enough. If I recall correctly (not guaranteed), the A4 only takes around 60A to crank. I use a small U1 size battery (PWC/motorcycle) as my start battery, and they typically have less than 300CCA.

[Bayou Sailor]

That's pretty much what I figured. Thanks Ed.

[roadnsky]

With only 2 total batteries, you might want to consider having them BOTH the same (size and output) if you have the budget.
Gives you a much more flexible setup.

As Neil likes to say, "I just love spending other guy's boat bucks!"

[Al Schober]

Not sure why you want AGMs. I could never justify them for my boat.
My Tartan 30 originally had two Gp27s with one of those A/B switches. One battery for house, one for starting - or something like that.
At some point I decided I wanted more house capacity. I doubled the house capacity by adding a Gp24 for starting, leaving the two Gp27s for house use. The final configuration had On/Off switches for both banks. The alternator fed the house bank. A combiner (voltage controlled relay) fed charge current to the start battery. Worked well.

[Sam]

Following up w/Al's comments the better deal crank per buck is with deep cycle lead acid w/750cca. I switch over to two Optima Blue top AGM dual purpose mainly because they were each about 10lbs lighter and much easier for me to handle during winter layup removal, spring commissioning and winter storage/maintaining etc. [That's the advantage - cost is disadvantage] Both still going strong - one from 2008 and other 2018. Fyi, I still keep one old Lead Acid Delco Voyager deep cycle to power a auto bilge bump during spring commissioning work in the yard.

[ndutton]

Bayou, please describe your regulation setup for all charging systems: shore power, engine alternator and solar.