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I feel like I'm overloading the board with all these posts, but here's another one.

 

My used boat came with two deep cycle batteries.  The previous owner said I would need a third if I was going to use the trolling motor for something like the whole day. But evidently he started the boat with the deep cycle battery.

 

If I was to get another battery, wouldn't it make sense to get a cranking battery, and save the two deep cycle batteries for the trolling motor (and everything else)?

 

Is hooking the deep cycle batteries in parallel a viable option, to prevent the need for switching, or is that a bad idea?

 

One more question: I was also thinking of installing some permanent float chargers for the batteries so I can just plug the boat in when I get it back home. Is that a thing?

 

Thanks,

Bill

 

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Your two deep cycle batteries should only be for the trolling motor. A third deep cycle battery can be used for engine starting and all electronics. The trolling motor can cause interference if electronics are connected to the same batteries. An onboard charger is a good idea to keep your batteries fully charged at all times.

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I agree with everything @Scott F said.  If you have a 12 volt trolling motor you can run off two deep cycle batteries wired in parallel.  I did it for years.  I would recommend that you buy two new identical batteries before you do this.  Running two batteries of different ages or strength in parallel can cause problems.  I used to run my electronics off of my two parallel trolling motor batteries without any problems but many people do have interference problems when running the trolling motor.  

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So it's not a problem cranking with the deep cycle battery?

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What voltage is your trolling motor?

All your batteries need to be marine deep cycle 12V batteries. 

You have a older model OB, 115hp inline 6 Merc that should have a alternator that charges the cranking battery, usually a group size 24. Your sonar unit should share your cranking battery. Depending on your TM voltage 12 or 24 or switchable 12/24 on some older models will determine the number of batteries needed.

This brings the next question, do you have a onboard battery charger?

Tom

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The TM is a 12V.  No onboard battery charger.

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1 hour ago, billmac said:

The TM is a 12V.  No onboard battery charger.

The reason most bass boats have 2 trolling motor batteries is to achieve 24V and double the amp hour usuage. 24V draws 1/2 the amps that a 12V battery does per hour.

You might want to consider upgrading the trolling motor to 24V if you have compartment space for 2 group size 29 to 31 size batteries. Using 12V batteries wired in parallel will double the amp hour use verses 1 battery the same size.

Remember you use the TM for 90% of your fishing time, it's a essential component.

If you have room for 1 trolling motor battery get the largest size that will fit the space; group 31 should last all day under normal use.

You will need a battery charger!

Tom

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To answer your question, can you use a deep cycle battery for cranking the battery?  The answer is yes and it may never create a problem for you, but it's not advisable, here's why.

Due to the plate design of deep cycle batteries, they deliver a small to medium amount of current over a long period of time, but they will not deliver a large amount of current for a short time.  It's not uncommon for a six cylinder outboard to draw 200-300 amps for the initial cranking load, and that's demanding about the absolute max a good deep cycle battery can give, but it gets the motor to spinning.  Now, here's where the problem comes in.  If the battery is not real good and almost fully charged, the voltage is going to drop drastically.  It may still be turning the motor over slower than normal, but the voltage may be too low for the ignition system to fire, and the motor won't start.  Also, on a cold morning, a battery will not deliver it's full amp capacity, (that's rate the cold cranking amps) so you even though you may have a good deep cycle battery, it still may not crank the engine.

 

In bass boat's, you normally run a dual purpose battery, one that can deliver the CCA needed, but also live through the numerous charges and discharges they go through running the electronics, pumps etc.

 

It's also not real smart to run the cranking battery in parallel with the TM battery.  I see people doing this quite often running 36V TM's and don't have the space for four batteries.  TM batteries are getting used and not recharged by the motor, run too long and you may find your motor won't start because the batteries are too low.  Several miles from the ramp, and no other boats around, you might be up that stinky creek.  

If thinking you can't run a 12V system on a 36V battery bank, you can.  The motor and electronics just connect across ONE the three batteries, not across the whole set.  The motor is also trying to keep that one battery charged, but sometimes that may not be enough.

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Other than cranking, what is the order of current usage by a typical boat's accessories? If I had to guess, I'd say trolling motor, livewell, then fishfinder.  I have two livewells but I don't think I'll be running the smaller one, which is really just a bait livewell.

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Pumps pull 3-5 amps normally, but are only running intermittently.

Depth finders only pull 1-2 amps normally.  They could run a week and not drain a battery.

TM's are the current hogs. On slow you are probably pulling 5 - 10 amps.  On high, that can be 25-55 amps, depending on the size of the TM.  On max, you might get 45-90 minutes, again depending on the battery and TM

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8 minutes ago, Way2slow said:

TM's are the current hogs. On slow you are probably pulling 5 - 10 amps.

I forget where I got the info, but my Endura C2-30 pulls at indicated speeds -

Speed 1 - 8 amps

Speed 2 - 10 amps

Speed 3 - 14 amps

Speed 4 - 20 amps

Speed 5 - 30 amps

 

A little searching for your model will get the info you need.

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Just remember......your cranking battery should be a dual purpose battery.  That battery is dedicated to starting your big motor and running ALL of your accessories/bilge & livewell pumps/lights/electronics, etc.  

 

Your TM being a 12v only "needs" 1 battery but would last longer with 2 batteries wired in parallel.  If wired in series you will fry your TM because it will be getting 24V.  NOTHING else gets wired into the TM battery(s).  They feed your TM only.  

 

Depending on how many batteries you choose to go with, it is advisable to get an on-board charger that has a charge bank for every battery including your cranking battery.  Unless you make very long runs, your outboard will never generate enough to recharge your cranking battery.  If you use a portable charger, you just hook it up to the batteries one at a time until they are all charged.  

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Quote

2 trolling motor batteries is to achieve 24V and double the amp hour usuage. 24V draws 1/2 the amps that a 12V battery does per hour

Not sure if this is what you're saying but putting a second 12 V battery in series with the first won't give you twice the run time; the current rating (and therefore run time, given the same load) stays the same, assuming identical batteries.


But yes the 24 V motors seem to draw slightly less current than 12 V motors (for example, MK 55# 12 V draws 50 A max, while 70# 24 V draws 42 A max). But to really double the run time add another two (series) batteries in parallel with the first two series batteries. Bow's getting heavy now so just balance it out with a 250 hp on the back :laugh7:

 

 

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On 2/18/2019 at 1:37 PM, billmac said:

So it's not a problem cranking with the deep cycle battery?

Only if it doesn't start! I would just have one battery for the gas motor and one for the troller if it's 12v. Fish a few days and see if it will last. Adding more batteries adds more cost, which is my limiting factor 100 percent of the time. I've been fishing with one half shot trolling battery (24v) for 2 years plus and I still get a bite every once in a while . I can still use the troller for about 5-6 hours . I will probably replace the crap battery once and for all the days get good and long . I've had 24 v for about 10 years and I miss 12v

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24 volt TM setups run on 1/2 the current of a 12 only if they don't develop more thrust.  If they develop more thrust and you use it they are doing more work.  If you never use their higher thrust capability, or use it rarely, you will see an increase in time to discharge.  But it's not quite as clean as "twice."

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Should my batteries be AGM?

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Before getting all twisted around about 12v vs 24 and one how one pulls half the amps as the other an all that other confusing stuff.  Forget about all the amp stuff and just remember this.  Energy used is in watts, the bigger the TM, and the faster you try to run the TM, the more watts it takes.  How many watts it takes is totally dependent on the Size of the TM and load the TM is under.  The load it's under is dependent on the conditions and how heavy and how much hull drag the boat has, and how fast you are trying to pull/push it.  None of that's going to change, if you want to go 3mph, doesn't matter if you have a 30lb thrust or an 107lb thrust, it's still going to take approx. the same amount of watts to go 3mph.

Now, without getting into all the equations and math to understand Watts.  Just understand watts is a directly proportional ratio of volts and amps.  The more volts you have, the fewer amps it takes to make watts.  The fewer volts you have the more amps it takes to make watts.  Nothing is going to change that.

So, if you have two batteries hooked to you TM, be they in series for 24 volts or parallel for 12 volts, they are still only going to be able to produce approx. the same amount of watts to run the TM

So, you ask, why bother buying the more expensive 24 or 36 volt TMs, over a 12 volt.  This is where you start getting into efficiency because of the less current draw and internal resistance as the voltage is increased.  A 24 volt TM is approx. 25% more efficient than a 12 volt  Don't remember the exact numbers but I think the 36 volt TM is approx. 35% more efficient than the 12, that's a 1/3 more run time gained just by going to a higher voltage motor

As lithium battery technology improves, don't be surprised if you don't see higher voltage TM's, with safety being the only limiting factor, since water and voltage make a dangerous combination.  I also look for a new generation TM motor show up for the lithium batteries. like the stuff they are running in electric vehicles and RC planes etc.

Also, when you increase the battery amp hour capacity, with two or three batteries, you decrease the amp draw on the batteries.  As amp draw is decreased, the battery becomes more efficient.  When you are pulling heavy current from a battery, it's rated amp hour capacity goes way down.  A 105 amp hour battery is closer to being a 65 amp hour battery if a TM running on max is pulling 40 amps off it.

So, you gain 25% more run time just going from 12v to 24V and then you gain another 20%- 35% buy decreasing the load on the batteries.  That's why people run 24 volt and 36 volt TM's over 12V, and the fact that about the max you can get it 12V is 54lb thrust.

 

One other bit of gee-whiz info.  the Digital TM greatly increase run time at the when not running at or near max.   

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I'm on a facebook group for the I6 and they are saying No to AGM.

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Most older motors can run fine off AGM. I read on another forum that it's the charging that the motor does that can be an issue.  The charging is not "smooth" and can damage the battery.  The older motors can't charge the agm properly and that is why standard batteries are recommended. 

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In reality, only the newer motors and designed to run AGM's. 

That old I6 is definitely not.  It only runs about a 16 amp charging system and I can't say for sure, but I don't think it even runs a regulator, just a rectifier. 

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One of the best things I did was buy sealed Cabelas deep cycle batteries on sale. Now I never have to do any maintence to the batteries and they will never leak. On sale it came to around $100 each I believe which is the same price as regular batteries. 

 

I now need to replace my starting battery and I will buy a sealed battery for that also. 

 

 

Also, your if your motor has an alternator to charge the starting battery you need to use the big motor enough to charge it. I found that out the hard way. When I fish I use the big motor to get to my spots and then the TM 98% of the time. It wasn't enough to charge the big motor and next time I went out my boat wouldn't start because the starting battery didn't have enough juice. 

 

The boat had a 2 bank charge which charges the trolling motor batteries. I bought at $15 Black and Decker charger to charge the starting battery and that has worked great for years. 

 

If you can afford and have space I'd get 2 deep cycles for the TM and 1 starting battery.

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Big'un,

Are you going to get a regular cranking battery or a dual purpose?  DP batteries are freaking expensive.

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1 hour ago, billmac said:

Big'un,

Are you going to get a regular cranking battery or a dual purpose?  DP batteries are freaking expensive.

Do you have an academy sports nearby?

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No. Never heard of them. Of course, I don't really have anything near me.

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Understand, being a sealed battery does not make it an AGM.  The so called maintenance free battery is normally nothing more than a standard flooded cell battery with smaller plates to it will hold more electrolyte. A group 27 in those usually sell for a little over $100, depending where you get them.   The Adsorbed Glass Matt (AGM) is a totally different animal and a Group 27 in those can sell in the $200 to $300 price range, again depending on where you get them.

 

It was mentioned a Dual Purpose is expensive, that's because they are normally on made in higher capacity than el cheapo batteries.   A true deep cycle is actually more expensive than the dual purpose.  One little bit of info, if a battery has a CCA or MCA rating on it, it's most likelynot a true deep cycle since deep cycles are not intended to be use for cranking.

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