# Dual purpose battery, yes or no



## gunz (Jul 2, 2016)

I am trying to keep my boat light as possible but my deep cycle battery is dead. been running dual batterys (start and deep) till last night. I ran one battery deep cycle all night. Worked fine. When the power got low I pull started the 25 (had external pull cord so no issues there. 

Anyhow I am considering going dual purpose battery but wanted to ask the opinion of folks here. If my motor was not an easy pull start I would never consider it. But since I have the option to pull and electric start I though ti might be worth getting the opinion of the folks here. 

thanks


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## gillhunter (Jul 2, 2016)

If I was only going to run just one battery (and I run three), it would be a deep cycle. A trolling motor is really hard on a starting battery.


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## gunz (Jul 2, 2016)

Agreed. 

I guess I should have made that more clear.. They make a battery now that is both deep cycle and starting. Wondering if anyone has any feedback on them.


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## DaleH (Jul 2, 2016)

gunz said:


> They make a battery now that is both deep cycle and starting. Wondering if anyone has any feedback on them.


That's all I've use in my boats ... made with amps for cranking and heavier plates (deep cycle) to take a repeated discharge. Love them!

That said ... no, I have never run a trolling motor off them ...

As I'm a saltwater fisherman and use them to power the boat's electronics while the engine is off, fishing in rips/currents sometimes up to 1-mile drifts. Go back (on power) and repeat.


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## Bob Landry (Jul 4, 2016)

Dual purpose batteries are nothing more than heavier starting batteries, good for running lights and electronics. They will not hold up to repeated heavy discharges from a trolling motor.


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## jethro (Jul 5, 2016)

I run a deep cycle only for my starting and trolling battery and I use the trolling motor an awful lot. It's only a group 27 and I can run my Minn Kota 50lb thrust powerdrive all day long and it still fires my 25hp Merc. Like you I have a pull start backup but never seem to need it even when the battery is low enough to make the trolling motor noticeably weak.


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## onthewater102 (Jul 6, 2016)

Deep cycle all the way - especially if you have the pull start where you don't need to worry if you've run the battery down or not. Don't try to use a starter battery for the TM for all the cycling reasons already mentioned.


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## gunz (Jul 6, 2016)

jethro said:


> I run a deep cycle only for my starting and trolling battery and I use the trolling motor an awful lot. It's only a group 27 and I can run my Minn Kota 50lb thrust powerdrive all day long and it still fires my 25hp Merc. Like you I have a pull start backup but never seem to need it even when the battery is low enough to make the trolling motor noticeably weak.



This is what I was wondering about. My current deep cycle was given to me and its not much longer for this world. I killed it the other night and had to hand crack (started the first pull so not a big deal) but was wondering about these dual purpose batteries if anyone had used it for both trolling and starting. I know not to use a starting battery for the troll motor but these new batteries have me intrigued.


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## perchjerker (Jul 6, 2016)

there is nothing new about these batteries they have been around a long time

In your situation, it would probably work fine

I dont have any personal experience with them since I never needed one


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## gunz (Jul 9, 2016)

perchjerker said:


> there is nothing new about these batteries they have been around a long time
> 
> In your situation, it would probably work fine
> 
> I dont have any personal experience with them since I never needed one



I understand they aren't new to the market yesterday, But we had to run a deep cycle battery for trolling and a cranking battery for starting back in the day. 

its just newer technology (relatively speaking) that I have never ventured into before. With my motor being a little 25, I am going to give it a whirl. Nothing ventured, nothing gained.


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## jethro (Jul 14, 2016)

The only difference between deep cycle and cranking batteries are how thick the plates are. The materials are all exactly the same, just different construction. With thinner plates, cranking batteries have more surface area creating more available power for short bursts. Deep cycle batteries have thicker plates with less surface area and with thicker plates the battery can withstand more charging and discharging cycles. Every time you charge or discharge a battery the chemical process that occurs degrades the plates. Cranking batteries are not designed to be discharged to less than 70% capacity as that is really hard on the thinner plates. They are also designed to remain in a state of full or near full charge. If your engines charging system is robust, like road going vehicles or boats with large engines then a cranking battery makes sense since it's basically in a state of full charge all the time.

I actually do not know what technically makes a dual purpose battery, but I can only assume it's simply a marketing ploy to justify a higher price for getting less. Deep cycle batteries will work just fine for a cranking battery, especially with small motors. But a cranking battery will not work fine for deep discharging. It's lifetime will be significantly reduced. The only disadvantage of using a deep cycle for a cranking battery is it takes longer to charge due to less surface area. Our little tin boats with low horsepower motors can have a hard time keeping them topped off especially . 

I said a lot but what it all means is simply this: the difference in cranking and deep cycle batteries is nothing more than durability and longevity based on how hard it's used. If you are planning to discharge your battery 40-50% of it's capacity, like with a trolling motor or other accessories, then you need a deep cycle battery.


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