Small dedicated start batter Yanmar SB 12

[pmagistro]

Ok, looking to install a dedicated starting batter and isolate my house bank with a solenoid (house bank is currently used for everything). My engine is a Yanmar SB12. I ran a calculation using the spreadsheet linked below and came up with 135 cranking amps as a minimum battery size. That means that a 150 cca battery should be plenty big enough, unless I don't understand something here.

I am trying to find the smallest dedicated starting battery that will reliably start my engine. All charging sources (alternator and solar) will charge this battery first, and I will be able to jump start with the house bank if things get dire. So excess capacity shouldn't be necessary. I am imagining coming in with bad weather, early morning after an overnight passage, having run electronics all night under sail, no solar, no engine...and now the engine must start to get through the inlet, or off a lee shore, etc.

Sizing worksheet: https://www.google.com/url?sa=t&sour...sMTEoadL7c_rWV

Assumptions: 33 cu in displacement, never gonna sail someplace cold, engine uses 5w-40 oil.

Considering this: https://www.amazon.com/gp/aw/d/B00CGNCNPY/ref=mp_s_a_1_3?ie=UTF8&qid=1516047265&sr=8-3&pi=AC_SX236_SY340_QL65&keywords="150+cca"+batter y&dpPl=1&dpID=41gvHwxf2HL&ref=plSrch

Ok folks, please tell me why this is a bad idea, and what you would do instead! Thank you!

[Sailmonkey]

My humble thoughts here. Use an off the shelf group 24 start battery from the auto parts store. Connect nothing to it except the starter. It’s a common, cheap, reliable battery.

All of your charging sources (alternator included) should go directly to the house bank. The start battery should be charged by an ACR or an echo charger. The start battery requires very little charge to keep up with the draw from starting the engine.

[pmagistro]

I am hoping for something considerably smaller than the group 24.

[Sailmonkey]

I think the little battery you linked to could work just fine. I don’t get a warm fuzzy though from the description however.

[kenbo]

My concern/question is what is the chemistry of your house battery? Is the charging profile the same as the Lithium battery you're proposing for starting service? If not one or both battery banks will suffer. I agree with charging the house as primary and start secondary in parallel.

[Sailmonkey]

the battery seems to be marketed as a replacement for a lead acid battery, so hopefully has been configured to accept the normal voltages seen when charging lead acid.

[a64pilot]

The Amazon link doesn’t come up as a link, but is it a Lifepo battery, made from A123 cells?
I have used them to great success on Motorcycles where saving an ounce was worthwhile, but why on a sailboat?
Just stay with tried and true, and cheap lead acid.
However I’m making some assumptions here, so try to post that link again, maybe with a space.

[a64pilot]

On battery sizing, I feel sure a lawnmower battery would start my 44 HP 4JHE, but the day that I need to spin the starter for much longer than usual or maybe have to do several restarts while trouble shooting an air leak or something, it wouldn’t make it, so having way more than minimum battery may save your bacon one day when things don’t go as planned

[hellosailor]

What the monkey said.

If you have to ask ANY question about ANY type of lithium battery? That's the first warning sign that you should be looking elsewhere. Unless you want a whole extra charging system and a whole extra set of charging rules to follow and yeah, probably isolating the two system as well.

[pmagistro]

Ok, I hear concerns about lithium. Understood; I am not set on that route. Anyone had experience with a small lead acid (motorcycle/lawnmower/similar) aboard?

I feel pretty good about my CCA calculations. Unless someone sees flaws with my math, I am just looking for feedback on the smallest reliable battery you are aware of.

[a64pilot]

Maybe not this exact specific battery, but there are many LifePo motorsports batteries that weigh just a couple of lbs and will start a Harely and or liter sportbikes easily. They are a drop in replacement and have lived for years being charged at 14 V steady, no three stage charging. Less than 2 lbs and over 200 cranking amps
https://www.batterystuff.com/powersp...14L2-BS12.html

[john61ct]

"Smallest possible" and "reliably" are in opposition, unless you have the gear and knowledge to closely monitor declining state of health to eliminate unexpected failure.

Do you *really* need very small?

One of those jumpstarter powerpacks fits in a coat pocket will do the job, until it doesn't, maybe 5000, maybe 500 cycles?

You can just routinely crank off House, use the specialized one as a backup.

Other cheaper way to go is small lead batt 35AH? and just buy a new one every year.

[Ivansgarage]

I have had one of these Odyssey batteries in my plane for 13 years and still cranks my 4 cylinder engine. Sealed lead acid battery. You can not buy a better battery
than an Odyssey.

Odyssey PC925L Battery 154.00 dollars

https://www.batterymart.com/p-odysse...yABEgK3sPD_BwE

[john61ct]

Bingo! Great choice, at the other end of the cost spectrum.

Note this is not designed for deep-cycling, but for high-CCA cranking of smaller engines.

Lifeline and Northstar are also great AGM makers as well, but I don't know if they make Starters.

[hellosailor]

Well...That Yanmar is supposed to be a 12hp engine? I used a 17AH "Alarm and exit light" AGM battery to jump start a Volvo MD6, which is rated 10hp. I'd totally never call that the right battery for the job, but the engine fired right up and the battery never complained for years afterward.

So there's a right way and a kludge to do anything. If you are looking for just emergency starting, something like a 20A AGM battery with no CCI rating at all will do the job. $30 if you chase 'em down, $60 from the battery franchise stores. No wet acid, no fuss, long storage without problems, like all AGMs.

Or you can go to WalMart (some of the strongest warranties) and just buy a cheap WalMart battery of the size you can be happy with. They used to have a three-year flat exchange warranty on starting batteries. There are just SO many options that will work, it is mainly a matter of what you can find locally. In the right color, of course.(VBG)