# Dual purpose battery



## WALI4VR (Nov 5, 2017)

I don't understand how it's done. I thought Deep cycle plates were thicker and cranking plates thinner. Opinions or thoughts on these dual purpose? I'm replacing my 9 year old fleet farm resolute 31 batteries and am finding lots of "deals" on dual purpose. 

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## Stumpalump (Nov 5, 2017)

There are two types of marine batteries. Marine cranking batteries and deep cycle. At least that's how it's been. The dual use is a marine cranking battery. Most still refer to the marine cranking battery as a deep cycle but it's not quite as "deep" as a plain old deep cycle battery. Do you need to crank a big engine or run a trolling motor? Batts fail so fast I'd be tempted to buy Walmart car batteries with the longest warrenty over a short warrenty marine specific battery unless you pound the boat in off shore conditions all of the time. That's where all marine batteries shine. They are built tuffer. The case is stronger and the plates are held in better. The warrenty sucks because people let marine batts sit overnight while deeply discharged. That kills deep cycle batts fast, marine cranking batteries faster and car batts the fastest. Pick a poison.


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## WALI4VR (Nov 6, 2017)

Stumpalump said:


> There are two types of marine batteries. Marine cranking batteries and deep cycle. At least that's how it's been. The dual use is a marine cranking battery. Most still refer to the marine cranking battery as a deep cycle but it's not quite as "deep" as a plain old deep cycle battery. Do you need to crank a big engine or run a trolling motor? Batts fail so fast I'd be tempted to buy Walmart car batteries with the longest warrenty over a short warrenty marine specific battery unless you pound the boat in off shore conditions all of the time. That's where all marine batteries shine. They are built tuffer. The case is stronger and the plates are held in better. The warrenty sucks because people let marine batts sit overnight while deeply discharged. That kills deep cycle batts fast, marine cranking batteries faster and car batts the fastest. Pick a poison.


Well I've treated my 9 yr old fleet farm resolute deep cycles correctly and never taken that pair (24v) too low and recharged asap. I tent camp so I can go fishing cheap! I use the front and rear trolling motors sparingly and after 8 days of fishing the batteries are down to 50 to 55 percent. The cranking battery gets charged each day with the main motor (50 hp 4 cycle merc). 18 gal tank is just about gone after 8 days of fishing. From what you are implying these dual purpose are really more crank than deep cycle. I know the marine units will take a lot more pounding than an auto unit. But I need lots of TM capacity so it looks like I'll have to stay with the pure bred deep cycle. 

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## Stumpalump (Nov 6, 2017)

9 year testimony of what doing it right will do for battery life.


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## handyandy (Nov 7, 2017)

I'm in the boat of picking a new battery as well. My boat came with a interstate group 27 deep cycle it cranked the engine and ran the trolling motor as well. Don't know how old it was when I got the boat, but lasted me three years before starting to lose its juice much quicker than what it did. So I replaced it rural king was close and the battery prices were hard to beat. I have had good luck with their exide branded batteries in some vehicles so I figured I'd give their marine deep cycle a shot. Well its around two years later now maybe a little more and it's shot won't hold a charge anymore. I always put it on the trickle charger after returning home and parking the boat, just like I did with the interstate it came with. So I'm debating on just getting another exide from rural king once again close and best price, maybe mine was a fluke idk. Or now I'm considering an agm from sams club they have the best agm price. Not sure the AGM seems worth it, maybe I'll just pony up for another interstate they always seem to be good.


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## WALI4VR (Nov 7, 2017)

handyandy said:


> I'm in the boat of picking a new battery as well. My boat came with a interstate group 27 deep cycle it cranked the engine and ran the trolling motor as well. Don't know how old it was when I got the boat, but lasted me three years before starting to lose its juice much quicker than what it did. So I replaced it rural king was close and the battery prices were hard to beat. I have had good luck with their exide branded batteries in some vehicles so I figured I'd give their marine deep cycle a shot. Well its around two years later now maybe a little more and it's shot won't hold a charge anymore. I always put it on the trickle charger after returning home and parking the boat, just like I did with the interstate it came with. So I'm debating on just getting another exide from rural king once again close and best price, maybe mine was a fluke idk. Or now I'm considering an agm from sams club they have the best agm price. Not sure the AGM seems worth it, maybe I'll just pony up for another interstate they always seem to be good.


My question still remains. What exactly is different between deep cycle, cranking and dual- purpose batteries. Seems to me dual let u have your cake and eat it too! Or is another marketing scheme we are all falling for? 

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## handyandy (Nov 8, 2017)

I'm not entirely sure I think it's more of a marketing skeem. I haven't ever felt like having two batteries, for me one good deep cycle has always seemed to provide enough juice to start the boat thing, run the troller, and fish finder as long as I ever need to between engine start ups to run to some where else. I've never had a problem obviously until the battery goes south. Ideally I would/should have two batteries one deep cycle for trolling motor, fish finder, lights, and a cranking/accessories battery. But I just haven't cared to deal with wiring up two batteries so the deep cycle could charge while the engine is running but not drain off the cranking battery while the engine isn't running. 

The two types of batteries are completely different designs, sure I guess they combine features of both battery types. That way they work for both purposes, but I don't think a dual purpose will last as compared to just getting the correct type of battery for the application. Looked at my crapped out RK battery sure enough I didn't look close enough upon purchasing it, it's a dual purpose made it two years maybe. Now I'm trying to remember when I bought it. Think I will make sure and just get a true deep cycle this time, as my previous interstate deep cycle lasted for 4-5 years which is about all I think can be expected no matter the battery.


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## MrGiggles (Nov 8, 2017)

WALI4VR said:


> handyandy said:
> 
> 
> > I'm in the boat of picking a new battery as well. My boat came with a interstate group 27 deep cycle it cranked the engine and ran the trolling motor as well. Don't know how old it was when I got the boat, but lasted me three years before starting to lose its juice much quicker than what it did. So I replaced it rural king was close and the battery prices were hard to beat. I have had good luck with their exide branded batteries in some vehicles so I figured I'd give their marine deep cycle a shot. Well its around two years later now maybe a little more and it's shot won't hold a charge anymore. I always put it on the trickle charger after returning home and parking the boat, just like I did with the interstate it came with. So I'm debating on just getting another exide from rural king once again close and best price, maybe mine was a fluke idk. Or now I'm considering an agm from sams club they have the best agm price. Not sure the AGM seems worth it, maybe I'll just pony up for another interstate they always seem to be good.
> ...



I bought a G24 Marine Starting battery from Walmart in July for running a trolling motor. It was completely dead by October, would not hold a charge any longer. Had I known what a starting battery was from the get go, I wouldn't have bought it. It's basically an automotive battery with a tougher case.

I imagine that dual purpose is just a marketing term. I'm sure a regular deep cycle will start even the biggest of outboards without an issue.


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## handyandy (Nov 8, 2017)

The main difference with traditional lead acid flooded cell batteries between cranking batteries and deep cycle is deep cycle have thicker plates that can handle being discharge slowly and charged slowly much better than the thinner plates in cranking batteries. In layman's terms the thinner plates can release their energy quicker but don't handle being discharged and recharged slowly as well. So generally for the given battery size a deep cycle won't provide as many cranking amps as a similarly sized cranked battery. But most outboards especially the small to mid sized ones we use don't require a lot of cranking amps so a traditional deep cycle works fine for cranking them, and can handle being discharged running a troller or whatever, and then being recharged slowly better than a cranking battery. From what I'm reading on AGM batteries they don't fair so well with inconsistent charging rates, which most of us having older outboards of early 90's vintage or older the charging voltage/amperage isn't regulated all that well. So AGM doesn't seem like a good choice for me with a 1994 evinrude 70. Think I'm going back to a interstate group 27 deep cycle.


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## beetlespin (Nov 8, 2017)

I love my Optima's. 

No dealing with adding water =D> and at the end of a full day of use they are still as strong as when I started.

I have two for my 24v trolling motor, one for electronics, one for starting the 50hp Merc.

I use the Optima 8016-103 D34M which can be used for starting and deep cycle use.


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## handyandy (Nov 9, 2017)

beetlespin said:


> I love my Optima's.
> 
> No dealing with adding water =D> and at the end of a full day of use they are still as strong as when I started.
> 
> ...



They're nice, but I haven't ever had a issue with a normal deep cycle battery having enough juice to do what I need. That is until they go south which holds true for any battery. I was just disappointed buy the life span of my last battery, I've had good luck out of interstate batteries so I will probably go back to that for the boat deep cycle. I couldn't imagine spending the money on four optimas, that would be more money in boat batteries than what I have in my beater subaru for commuting to work :LOL2:


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## beetlespin (Nov 9, 2017)

handyandy said:


> beetlespin said:
> 
> 
> > I love my Optima's.
> ...





Take a flat bottom boat doing 30mph on the Delaware river with the the wind blowing against the tide and you'll appreciate the pounding these batteries can take. Wish my back held up as good :mrgreen: 

After destroying my Interstates these took their place. My last set of batteries lasted 5 years before they started showing signs of degrading. They were still OK, just didn't have the power left at the end of the day. They are now in my buddies boat.


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## handyandy (Nov 9, 2017)

The interstate I had took a pounding in my boat lasted 4-5 years before it began to become a little weaker on cold cold morning duck hunts which is when I replaced it. And went with a exide from rural king due to price, and ease of getting it. Well it hasn't fared so well around two years in if that, and it's done. So I'm going back to interstate now, last one held up in my boat flat bottom as well with lord only knows how many miles of towing on not so good roads, pounding waves in my flat bottom.


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## DaleH (Nov 9, 2017)

Stumpalump said:


> There are two types of marine batteries. Marine cranking batteries and deep cycle. *The dual use is a marine cranking battery.*


... and respectfully .... you would be quite wrong sir.

FWIW this info below comes from my boating friend, a PhD chemist and physicist, who makes batteries for US Navy torpedoes. Luckily ... he gives me his old 12V batteries they used for bench testing! Gotta spend that budget every year, you know!



WALI4VR said:


> What exactly is different between deep cycle, cranking and dual- purpose batteries. Seems to me dual let u have your cake and eat it too!


*CRANKING* - Plates/design optimize high load cranking amps, i.e., the peak cranking amps on a V6 OB starter is ~250-amps, dropping to < 200 whilst continuing to crank.

Purpose - Designed to discharge a large amount of energy for a short period, not designed to be deeply discharged. 

When such a cranking battery is deeply discharged, it can suffer damage that affects its useful life and capability to charge back to full capacity.

*DEEP CYCLE* - Typically used for static loads over a long time. 

Purpose - Designed to discharge a small amount of energy over a long period, often until most of the battery’s capacity has been fully discharged.

Deep cycles are built to discharge up to 75% of their capacity without suffering any damage. The 'safe' amount of discharge varies depending on who built it — some are designed only for a 45% discharge, while others can discharge 75% or more of their total energy capacity without any negative effects on long-term performance.

_Look at the difference between them by comparing a track&field sprinter vs. a marathon runner. A cranking or 'starting' battery performs like the sprinter, i.e., delivering lots of power before running out of breath. Whereas the deep cycle battery is akin to a marathon runner, offering far less speed, but for much greater endurance, i.e., time._

*DUAL PURPOSE* - A blend of both, a cranking/starting battery made with heavier plates, and designed to withstand a deep discharge.

Purpose - Designed for nominal cranking duties and minimal discharge use, sort of a blended use, if you will. 

Example, I would never use a dual purpose one to start a 300hp V8 OB motor, or inboard motor, nor would I personally run a 12V trolling motor on one. But I have used them on numerous dual or triple battery boats where we'll crank the V6 OBs with them, then run our electronics off the same battery whilst on anchor or drifting, i.e., motors off.

*IMHO the best value*, and my friend concludes this too, for 'general use' is a marine battery sold by Walmart. They are fresh, carry the month of manufacture on them and they are made by Johnson Controls, the same company that owns and sells Optima gel-type batteries. 

_To me it is prudent that a boater understand that they are really 3 distinct battery designs and applications._ 

TIP - For those running dual battery installs without an electric trolling motor, two dual purpose ones are awesome! But never run a 1-Both-2-Off battery switch on both, as they will equalize if/when you shut off the motor. What I do is use battery #1 on odd days of the week and #2 on even days of the week. Yes, you may have to check your iphone's calendar :roll: . 

Or, if you have long runs to your favorite fishing hole ... run out on #1 and back in on #2. Use cycles like this help equalize use, load and charging!


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## WALI4VR (Nov 9, 2017)

DaleH said:


> Stumpalump said:
> 
> 
> > There are two types of marine batteries. Marine cranking batteries and deep cycle. *The dual use is a marine cranking battery.*
> ...


Thank you Dale. 

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## water bouy (Feb 11, 2018)

I'm getting ready to wire up my 16 ft aluminum vee. My back is only good for 4 or 5 hours on fishing days which aren't that often anymore. Wonder if I could get away with a dual purpose using a 30 hp or 40 hp tiller electric start and a 50 lb trolling motor. By the time I stop fishing altogether I imagine the next generation of batteries will be here weighing nothing and doing everything.


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## vfourmax (Feb 13, 2018)

Even an actual "Deep Cycle" battery is capable of starting a motor depending on the amount of cranking amps the motor requires. 

I do know that a Napa #8231 deep cycle battery even though it is a larger group 31 battery is only listed as putting out 650CCA as it is a deep cycle and not a starting battery. 

That is sufficient to start a smaller engine I would guess most motors up to about 70 horsepower easily maybe even a bit larger but would not start most modern "big" motors that require a minimum of 800 or so cranking amps. 

I would check my engine owners manual for the required battery capacity in amps and also take into consideration what else I was planning on trying to run off of the same battery.

Personally I prefer to use the batteries for the trolling motor just for that purpose and all other uses off of a separate battery.

Just like anything else as boaters are using multiple and more advanced and larger electronics, running live wells, power poles and so forth consuming greater amounts of battery power the boater needs to have more and larger batteries to handle the consumption of juice.


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## water bouy (Feb 13, 2018)

I'm leaning toward an acm battery for the trolling motor. It'd be up front where most of the bouncing takes place. Then find a place for the starting battery in the middle of the boat. 

https://www.amazon.com/dp/B00K898AT6/ref=psdc_389574011_t1_B005CLPOQM


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