New Starter Battery

[skipmac]

Originally Posted by foggysail

I have many years in boating, first in a sailboat before moving to power. I have never had a performance problem using a deep discharge battery for engine starting. As to starting batteries, I purchased my FIRST last year for starting purposes only because it was far less expensive choice.

Anybody who believes that a deep discharge battery with an equal ampere hour rating that satisfies the engine's factory recommend battery size, cannot crank that engine does not know what he is talking about. Further he should not be advising others to not use them for starting purposes.

Foggy

I don't think anyone said you could not start an engine with a deep cycle battery. I've done it lots of times. When I bought my last boat it only had deep cycle batteries and cranked the engine dozens of times.

What is said, correctly, the design of a starting battery is optimized to put out a lot of amps in a short time; a deep cycle battery to put out fewer amps for a longer time (and also to better tolerate deep discharging). So, a smaller, lighter, cheaper house battery will put out more amps in a short burst better than a similar sized deep cycle battery.

Sure you can use a deep cycle battery to start an engine or you could even use a starting battery to run your house loads. You could also use the end of a ratchet wrench to drive a nail but a hammer does it better and costs less.

My battery set up is a bank of deep cycle batteries and a much smaller, isolated, starting battery for the engine. That way I get max use out of the house banks and don't worry about losing starting capability.

[nigellongland]

Sorry if I used the wrong word, ie D battery- I type I am discussing is the large, 150 pound battery that is 3 ft long-please tell me what type I need as a start battery, why 6 V are not good and do I need an expensive battery to start my engine vs a regular deep cycle battery with good amperage and Cold cranking amperage? thanks nigel longland

[skipmac]

Hi Nigel,

Hope you understand Bill was just kidding with you. The mental image of starting a diesel with a D size flashlight battery is a bit amusing. And you weren't exactly wrong, just left out a small detail. Large batteries can be D size but with a number in front, like 2D, 4D, 8D larger numbers = larger battery. I'm guessing you have a 4D or maybe 8D.

A couple of things to clarify for you. First your starter most likely needs 12V to operate. Yes you can certainly use 6V batteries but you need two connected in series so the voltage adds up to 12V.

If your current system has D size 6V batteries they are probably what are called "Deep Cycle" batteries. As noted in several comments, deep cycle batteries will certain start an engine but getting a "Starter" type battery would be better. A starter type battery will be:

1. cheaper
2. smaller
3. more efficient
4. overall be better for starting than big 6V, deep cycle batteries.

You just need to insure two things for either battery type:

1. The starter battery is isolated from the house loads like lights and such so it is not accidentally discharged and not available for starting.

2. If the starter battery is isolated from the rest of your battery system you will need to make sure that this battery is getting charged when the engine is running or the battery charger or other sources are operating.

Both of these are fairly easy to set up and are discussed in other threads on the forum. If you need to sort this out and can't find the appropriate discussions just mention it and I'm sure someone can find them and post the link.

[nigellongland]

thanks again and yes it is a funny picture of starting it with a flashlight battery. Yes it is a 12 V system, dedicated and separate system on the engine start battery. I believe the battery is old and 8D. Can you suggest a starter type battery , I will look to see if the engine manual says how large or cold cranking amps needed, would that be in there?- are there any general recommendations for how large a starting battery I need for this size /80hp engine? thanks again nigel longland

[skipmac]

Originally Posted by nigellongland

thanks again and yes it is a funny picture of starting it with a flashlight battery. Yes it is a 12 V system, dedicated and separate system on the engine start battery. I believe the battery is old and 8D. Can you suggest a starter type battery , I will look to see if the engine manual says how large or cold cranking amps needed, would that be in there?- are there any general recommendations for how large a starting battery I need for this size /80hp engine? thanks again nigel longland

First, suggesting a battery, depends on where you're located? What part of the world are you in as most brands I know of are local.

The size or CCA capacity is a good question and maybe someone else can chime in here. I could not find that in my engine manual so made a semi-educated guess based on what I read others with similar size engines would use. Also depends to some extent on temperatures when you're boating. If you live in Denmark and use your engine in late fall when it could be 0 degrees C you might want more battery than someone in the Bahamas where it could be 35 degrees C.

I have a 60 HP diesel and went with a Group 27 starting type battery which come in 750-800 CCA ratings. I think that should do for your 80 HP diesel as well but might want a second opinion.

[nigellongland]

OK, so thanks to all for the discussion. I have learned a lot and read a lot - maybe now have a better idea. Clearly a starter battery is used to start engines given its design, and deep cycle can be used for starting but is not designed for that, but for longer term slow use not quick bursts of power. I have found I actually have 4D battery not 8D. So after all your help I am planning on buying a well known brand, starter battery not deep cycle. Still not sure how large though to go. Can you explain what a group 27 battery is? thanks to all nigel longland

[nigellongland]

And to Belizesailor, are you in Belize? where. I spent lots of time there and in Honduras also nigel longland

[skipmac]

Originally Posted by nigellongland

OK, so thanks to all for the discussion. I have learned a lot and read a lot - maybe now have a better idea. Clearly a starter battery is used to start engines given its design, and deep cycle can be used for starting but is not designed for that, but for longer term slow use not quick bursts of power. I have found I actually have 4D battery not 8D. So after all your help I am planning on buying a well known brand, starter battery not deep cycle. Still not sure how large though to go. Can you explain what a group 27 battery is? thanks to all nigel longland

Group 27 or 4D, 8D, etc refer to the physical size of the battery, which will also roughly determine the battery capacity since bigger, heavier batteries can hold more lead so more total capacity.

A group 27 will be about 12.6" L X 6.75" W X 9" H. A 4D about 20.6" X 8.6" X 10".

[barnakiel]

Originally Posted by skipmac

The size or CCA capacity is a good question and maybe someone else can chime in here.

I think I have read in Compton's book that 2-3 CA per 1 cu inch is a good base measure. He equals this to minimum of 250 CA on a 2 liter diesel engine.

Some boat maintenance books say that a battery should not drop below 80% of nominal voltage while cranking - 9.6 Volt if you have a 12 Volt starter. If the voltage drops below that, your battery may be too small or too old.

This all applies to cranking a sound engine with no issues in warm climate. Add cold, periodic need for purging the air from fuel lines, etc. and you get the picture.

b.

[btrayfors]

Nigel,

I'd go with a Group 31 starting battery. Plenty of cranking amps for your 80hp diesel, and smaller and lighter and cheaper than the 4D you have now.

No joke :-)

Bill

BTW, for amusement, there are some incredibly small batteries...not much larger than a D-cell flashlight battery....which are actually capable of starting big diesels. They're used in special situations....light racing cars, etc.

B.