Marine Batteries

[Adam1]

I have a two Marine Starting Batteries that I would like to change next season with Deep Cycle ones. The issue is that the CCA for a Deep Cycle Battery is generally much lower than that of a Starting Battery of the same grouping. I'd like to use a Deep Cycle Battery having the same or higher rating as the starting batteries. The Starting Batteries that I'm currently using are each rated as follows:

27M - Group Size
1000A - Marine Cranking Amps (MCA)
800A - Cold Cranking Amps (CCA)
125 - Reserve Capacity (RC) Minutes
9.5 inches x12.75 inches x6.875 inches (HxLxW)
57 lbs

The Deep Cycle Batteries are DieHard Platinum Marine Batteries having the following ratings:

31M - Group Size
1150A - Cold Cranking Amps (CCA)
205- Reserve Capacity (RC) Minutes
9.5 inches x13 inches x6.8 inches (HxLxW)
75 lbs

Questions:

Do I need to stay with the same group size that I'm currently using?
Are there any downsides to going with a battery of a different grouping albeit slightly larger and much heavier?
Will the Deep Cycle Batteries perform at optimal levels given that they would be used as replacements for the smaller Starting Batteries?

Thanks in advance for any insight on this topic.

 

[Lazy Daze]

Yes, you can mix and match different sizes (24, 27, 29, 31, etc) of batteries with no problems. You can even mix and match starting and DC. I'm assuming you have the typical battery selector switch?

Is there a particular reason you're upgrading to two DC's?

FYI, the normal sized starting battery used with your engine would be a Group 24.

 

[Bucit]

BTW, your post shows that the CCA for the deep cycle battery to be higher than the starting battery where as you made mention is much lower? Why not keep a starting battery for just that and install a deep cycle for all DC options. This way you have a dedicated battery to always make it home on.

 

[magstang1]

Cranking amps and reserve capacity are inversely proportional.

The batteries have plates in them to create a chemical reaction which in turn produces DC current.

A higher quantity of thin plates with a greater surface area creates more initial energy, or cranking amps.

Larger plates with more mass create a longer run time.

You can see that the physical size of the battery limits the power output.

As a rule of thumb, it takes one cranking amp per inch of displacement to start an engine. 350 Mercruiser would require at least 350 cranking amps to start.

Plates erode, or sulfate inside the battery necessitating additional power when it is new for longevity sake. Your 1000cca battery won't stay at 1000cca for ever. Additionally, batteries are used to support auxillary loads while not being charged so they need reserve capacity for that.

Don't get too caught up in trying to match the numbers exactly.

Edit to add:

After rereading your original post, I would like to add some information.

Most marine batteries are considered a dual purpose battery, meaning that the plates inside the battery are somewhere in between thick and thin.

If you use a purely deep cycle battery as a starting battery, you can damage it. Trying to draw the large current from a small surface area can erode or sulfate the face of the battery plates. This essenially creates insulators on parts of the plates, further reducing it's capacity. A long, slow draw does not shock the surface of the battery plates.

Hopefully this helps you understand what all those numbers mean, and in turn helps you decide what battery you should choose.

Larger group size means more power. Deep cycle versus starting means how much power is available for the specific load type.

 

[Adam1]

My thinking is that if I can achieve the same CCA or higher with a Deep Cycle Battery by going to the next group size, I would be better off since Deep Cycle Batteries will allow you to discharge them to a much lower State of Charge and yet are able to regain their full charge without memory. And this can be repeated presumably numerous times. If I were to stick with the same group size, the Deep cycle battery generally has a lower CCA than that of the Starting Battery which may not start my engine.


Going with a one of each (Deep Cycle and Starting) and switching between the two might be a viable option but why do it if one can get the Deep Cycle Battery with the same or higher CCA albeit using a higher larger size.

Any comments to my reasoning?

 

[Go Aweigh2452]

what magstag stated plus deep cycle are designed to be depleted where starting batteries are not. Deep cycle batteries are optimized for long slow current draw and deep extended period dicharges for running accessories. They can be used to start the engine but will not be as effective in some cases.

The starting batteries are optimized for large brief current supplies for engine starting. However they will sulphate easily if left discharged and become less effective.

The answer to your question must be based on how you intend to use the battery. Many boats employ separate banks of batteries, some for starting duties and some for house loads. If you intend to overnight or raft up all day long with accessories running, you'd be best served by having an isolated bank of house batteries of the deep cycle type to draw from. Meanwhile, your engine starting batteries would remain fresh. This is accomplished through the use of a battery isolator which is just a large diode that allows your alternator to charge all the batteries, but won't allow your starting battery to discharge anywhere except to you starter. Since batteries of different types don't like being mixed in a bank too well, another popular solution, amongst large yachts anyway, is to use the alternator from one motor to charge exclusively the house batteries, and the other motor to charge the starting batteries. This ensures that they charge at the proper rates and achieve the proper voltages to burn off the sulfate, and keeps them fully separated to avoid any electrical gremlins.

 

[Lazy Daze]

I think you're over thinking this. Keep it simple.

Grab a group 24 (starting) with about 700 MCA. Forget about CCA as it's a virtually useless criteria for bowriders - unless you're boating when it's freezing cold outside. You have a small block V8 - the engine itself doesn't require a whole lot of juice to turn it, but you do need some extra amps because of the fuel injection system/ECM.

Next, get a group 27 (or higher, if you prefer) DC for when the engine is off and you're blasting the stereo and making margaritas with a 12v blender. A group 27 will last a long, long time. A lot longer than most think.

Again... assuming... you have the standard battery switch, you won't need to do any re-wiring, either.

 

[Adam1]

Thanks to all who have provide me with feedback/ advice. I will most likely replace with the same OEM batteries that were installed.

 

[Lazy Daze]

Sure, but to be honest, two 27's are overkill. You're just spending more money than you need to. Just because it came that way (assuming you are the original owner) doesn't mean it's right. One group 24 would have been the typical "standard issue". However, Sea Ray doesn't provide batteries - that's up to the dealer.

 

[Adam1]

Dennis,

Is there a battery size selection guide that Dealers use to match batteries to engine size? Just wondering how Dealers go about choosing the right size battery for the job given that Sea Ray doesn't provide batteries.:huh:

 

[kaz911]

I have Sea Ray / Mercruiser installed Optima AGM batteries (Blue Top) - they are the only ones I have. In general (IMHO) AGMs preform better and can be used as deep cycle batteries. And they have more than enough juice to start the engines. They charge faster and last longer than normal Lead Acid batteries.

My favourite Batteries are Lifeline AGM's. If you search here and on THT you can see lifetime reports of up to 9 years.. (And they come with prorated 5 year warranty). Once my Optima's kick out (2 or 4 are 1/2 bad already) then I'll replace them with Lifeline. I am not affiliated with Lifeline!

Btw. if you keep your boat on a trailer - you won't have anything else than stereo memory using power while you are not using the boat. If you are in salt water all season - then the MerCathode's will burn about 100-200 mA constantly.

 

[Lazy Daze]

Dennis,

Is there a battery size selection guide that Dealers use to match batteries to engine size? Just wondering how Dealers go about choosing the right size battery for the job given that Sea Ray doesn't provide batteries.:huh:

Somewhere there is a guide from Mercruiser, yes. I haven't seen it in a while, though. It might even be in the Merc installation manual that came with the boat, but I'm not sure. I just remember that small block MPI's need about 700MCA, carb'd engines about 500MCA and big blocks need about 850MCA.

For what it's worth, on my Sundancer (fridge, extra lights, head system, etc) I use a group 24 starting and a group 27DC for when we overnight. All this being said, it's certainly OK to go with a higher-amp-rated battery. My group 24 (starting) has a MCA of 1000. But, we only carry two models of group 24's (keeps it simple). The first has an 800MCA rating, the second has the 1000MCA. The cost difference is only about $10, so that was an easy choice for me. Now, I'm no battery expert - but it's my understanding that batteries will last longer when used for their designed purpose... a starting battery for starting the engine and a DC for extended use with engine off.

 

[vandal]

Go over to Lee Battery on rt 70 up road from MM brick and they will have every thing you need that is where MM gets batterys from.

 

[Lazy Daze]

Just thought of something... Adam, you don't have DTS, do you? I didn't think you did, but if you do then the requirements are different. If anybody with DTS, AXIUS or ECT engines is reading this (gas engines), your requirements are as follows (this was an update by Merc earlier this year): 1000MCA and 180min Reserve capacity. This is because of the higher electrical demand from those systems.

 

[Adam1]

Lifetime reports of up to 9 years.. (And they come with prorated 5 year warranty).

Lifeline's lifetime sounds to good to be true. The longest warranty I've seen on marine batteries was 3 years (Sears Marine Platinum Diehard), so worth looking into. Thanks.

 

[Adam1]

Small block MPI's need about 700MCA, carb'd engines about 500MCA and big blocks need about 850MCA.

Dennis,

Thanks for the info. I was told that mixing different battery technologies (two batteries, one Starting the other Deep Cycle) isn't a good idea and could shorten their life? Any truth to that?

 

[Adam1]

Go over to Lee Battery on rt 70 up road from MM brick and they will have every thing you need that is where MM gets batterys from.

My current batteries are LEE. I don't know who makes them but I believe LEE imports them from China and puts their label on them.

 

[Ike]

Just a tip. Stop thinking in terms of Group size. If you look it up you will find out that Group size indicates only two things, the physical dimensions of the battery and where the lugs are, on top or on the side. It has nothing whatsoever to do with the battery capacity. The best way to go to a large capacity is to ask what the Amp Hour rating is , or the reserve capacity. Neither are labeled on the battery but should be listed on the spec sheets. Going to a higher Amp Hour rating will give you greater capacity.

Most of the advice here is correct. Stick with a starting battery for starting your engines, and a deep cycle battery for running electronics. Watch out for batteries labeled Marine, or even Marine Deep Cycle. These are more often than not hybrids, that is they have a combo of thick and thin plates, so they can be used as both. They are fine for most applications, but if you have an extensive electrical system you want true deep cycle batteries which have thick plates. Golf Cart Batteries (6V) are true deep cycle batteries. There are also 12V true deep cycle batteries, but they typically cost a lot more than "marine" batteries. Go to an RV store like Camping world and buy 12V deep cycle batteries that are used for house loads in RVs. See a lot more on batteries at Batteries: Everything You Need to Know http://newboatbuilders.com/docs/BatteriesEverything.pdf

 

[Adam1]

Just thought of something... Adam, you don't have DTS, do you?

Dennis,

No I don't have DTS (would have liked to). But, thanks for the info. nonetheless.

 

[Lazy Daze]

Dennis,

Thanks for the info. I was told that mixing different battery technologies (two batteries, one Starting the other Deep Cycle) isn't a good idea and could shorten their life? Any truth to that?

No. Not in the way that you are/will be using batteries. Or me, for that matter.

I'm not against AGM's, so please don't take my comment that way... Just take into account how much the AGM costs and it's lifespan vs cost of lead/lifespan.

To add to what KAZ said in regards to what things will draw power when engine is off... Also the bilge pump (even if it's not pumping it draws a little bit) and your ECM will draw power all the time. Even with all 3 of those things (radio memory #3), it's still a very small amount.