Best Starting Battery Size?

[BSquared]

I've got several hundred pounds (well, perhaps several dozen pounds ) of dead batteries as a result of neglecting the boat somewhat over the past couple of years, and now I'm going to have to replace them. I think this time I want to go with a minimalist approach: the smallest house and starting batteries that are practical. The house-battery size I can calculate, but what's a good size (in amp-hours, cold-cranking amps, or whatever) for a starting battery for an Atomic 4? Any specific recommendations for a particular battery for this purpose?

[Don Moyer]

BSquared,

I'm not sure what's behind your minimalist approach, but in preparing a recent tech note on the subject of battery and alternator selection, I researched several documents (mostly Nigel Calder's text "Boatowner's Mechanical and Electrical Manual") and came up with the following rules of thumb:

1) In terms of sizing batteries in cruising sail boats, Calder recommends installing the largest battery bank that space (and budget) permits, and to then connect the batteries in such a way that allows you to isolate one battery to be used later for starting.

2) An equally simple rule of thumb for alternator sizing follows from the first rule: alternator output should equal approximately 25% of a boat's total battery capacity in amp-hours.

3) Keeping all batteries the same size and type can greatly simplify the process of managing the use and charging process. I personally do not see the value in incorporating a different type of battery for starting the Atomic 4. The low compression design of the Atomic 4 allows it to be started with ease using any normal size deep cycle "house" battery.

Don

[BSquared]

Thanks very much, Don. I think I'll use Calder's calculations to figure the house-battery size and get two gel-cells or AGM batteries that size. Glad to know the A4 doesn't require a special "starting" battery.

By the way, what's behind my "minimalist" approach is weight and bulk. I started out with two gigantic 6-volt golf-cart batteries, assuming fairly long cruises without running the engine, and then a fairly large starting battery as well. The batteries were very hard to slog around (moving in and out of the boat for winter layup/spring startup and so on), put a huge strain on the alternator, and generally were a pain in the whatever. And, of course, there was no way to keep *all* the acid inside and I've got the holes in my pants to prove it. I've realized I'm really an overnight cruiser, and now that the batteries are thoroughly dead I can resize the batteries to match my true cruising style.