Small dedicated start batter Yanmar SB 12

[a64pilot]

I used to only use Walmart batteries in my little Dive Boat.
Every other year I would replace them and the take outs went into the RV, ones in the RV were turned in.
Never had a battery problem, ever, but I wasn’t full timing either.

[john61ct]

Fact is, cranking an engine is just not a challenge, many ways to go, all will work fine.

Only those looking for "the best" way (for their situation) make the question interesting.

[CarlF]

Consider an Optima red top size 35. An AGM starting battery not a deep cycle battery. Weighs 31lbs. 910 cranking amps. I keep one in a locker with jumper cables as a “Plan C” way to start the engine. I charge it once a year. It’s seven years old amd tests great.

[Cheechako]

an automatic charger module for about $60 and up can be used for your start battery in lieu of the solenoid.

[pmagistro]

Cheechako, not sure I follow you.

CarlF, that's more or less the opposite of what I need....I'm looking for a battery that fits into the space available, roughly 8"l x 5" w x 5"h, and I definitely don't need 910 cranking amps.

John61ct, as for if I need small....no, I need the smallest battery that will consistently amd reliably do the job. My engine is tiny, and in outfitting a barely 30' boat for long term and offshore cruising, space matters, so I don't want to dedicate more weight and space to batteries than I need. If I am going to beef up the bank, it will be the house bank, and before I do that I would be adding more solar as well as wind generation. I just want an isolated system to start the engine.

[Cheechako]

Automatic Charging Relay.
Blue Seas seems to dominate a google search, but those I've had were from a small family company for a couple decades and only $59. Install it, it automatically charges your starting battery when you run your engine aside from charging your main bank with no switching.

[Wotname]

An SB12 does need much current though the starter motor if you intelligently use it's decompression lever and take advantage of it's fairly large flywheel.

Decompress and use the starter motor to build up RPM, then release the decompression lever.

Just about any old flat battery will work when doing it this way.

[john61ct]

The Optimas svck since Enersys sold the brand off to Johnson Controls, definitely not good value anymore.

But of course they will start an engine

[pmagistro]

Originally Posted by Cheechako

Automatic Charging Relay.
Blue Seas seems to dominate a google search, but those I've had were from a small family company for a couple decades and only $59. Install it, it automatically charges your starting battery when you run your engine aside from charging your main bank with no switching.

Gotcha. I have used the powerstream solenoid in the past, bit I like yhe BSS ACR you are referring to. The issue is, right now I don't have a dedicated starting battery. I have a small space that I can put one, but not enough room for another group 24 (like the house bank) without making other sacrifices.

[pmagistro]

Originally Posted by Wotname

An SB12 does need much current though the starter motor if you intelligently use it's decompression lever and take advantage of it's fairly large flywheel.

Decompress and use the starter motor to build up RPM, then release the decompression lever.

Just about any old flat battery will work when doing it this way.

Good tip, Wotname! Thanks.

[pmagistro]

Quick update. I tried an Everstart cheapie from Walmart, 275 cca group size U1 battery. It will start my SB12 cold, but only with the alternator disconnected. I found a nice little nook for a group u1 battery and would love to make one work. So I need to figure out how many additional cca I need to start the engine with my alternator and/or what is the biggest U1 battery available (in terms of CCA). Note: one 65ah group 24 with 675 mca (about 520 cca) starts her up just fine.

[Sailmonkey]

Originally Posted by pmagistro

Quick update. I tried an Everstart cheapie from Walmart, 275 cca group size U1 battery. It will start my SB12 cold, but only with the alternator disconnected. I found a nice little nook for a group u1 battery and would love to make one work. So I need to figure out how many additional cca I need to start the engine with my alternator and/or what is the biggest U1 battery available (in terms of CCA). Note: one 65ah group 24 with 675 mca (about 520 cca) starts her up just fine.

When you say with your alternator disconnected, you mean with the belt removed?

If that’s all that’s the problem, why not fish out the field wire and put a disconnect in it. The unexcited alternator shouldn’t cause any extra drag.

[pmagistro]

Originally Posted by Sailmonkey

When you say with your alternator disconnected, you mean with the belt removed?

If that’s all that’s the problem, why not fish out the field wire and put a disconnect in it. The unexcited alternator shouldn’t cause any extra drag.

No, I've already done what you suggested. I have a disconnect switch on the lead from the alternator.

I can use this little battery to start the engine with the switch turned off, but ideally I don't want to add opening the engine compartment, switching off the alternator, starting the engine, switching back on the alternator, then closing up the engine compartment on account of too small of a battery.

[a64pilot]

If your cutting it that close, that gives you no room for the battery to age and lose capacity etc.
I forget, what is the purpose here? Inexpensive I assume? Get a used battery, for next to nothing at a junk yard.
If it’s weight and size, get one of the Lithium based motorcycle batteries I linked to, maybe 1lb will easily start a 1L Superbike, it will certainly start a 12HP Diesel.

[a64pilot]

Like this one, there are bigger of course, maybe a Harley battery for instance. But seems to be roughly 100 CCA per lb
https://www.denniskirk.com/2009245.s...d=244288899576