# Battery size choices



## firecat1981 (Nov 27, 2007)

It's been a few years since I bought my last battery and I've been looking around a bit. On my new build I'll be running 2 12v batteries parallel (not in series, I need more capacity not 24v).

Looking at newer offering it seems they've upped the amp hr ratings on group 24's while group 27/29's have stayed the same.

Example. Everstarts group 27DC has 750 cranking amps and 109amp/hrs @1amp. That's close to the last one I bought.

Now the group 24DC has 690 cranking and 101amp/hrs @ 1 amp. (In the past I think they were rated around 80 amp/hrs)

That seems very close to me, so why would I choose the heavier group 27?


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## Vertigo (Jun 3, 2012)

Lead acid battery technology has not changed much. What has changed is advertising hype. Of two batteries, *both using the same technology*, the biggest one wins.

Why would you want to run in parallel? If one battery goes bad, it will drag the other one down. Better to use a battery switch and work from one battery at a time.


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## lemaymiami (Feb 9, 2007)

Amen... you must keep battery #2 isolated so that if you run down #1 (or it's just not holding enough juice and needs a boost to get you started again (and charging...) you still have #2 in reserve, period. If you're pinched for money and can't afford a battery switch - just having a second batt that you can attach to will make all the difference in a bad spot...

I won't rig a skiff without two batts, and a battery switch - it's just not a good practice to only have one batt on the skiff - and once again - keep them separated. You can switch the batts so that you have them combined just long enough to get your motor started then go back to a single batt (#1 or#2) as soon as you're up and running - you'll be glad you did...


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## firecat1981 (Nov 27, 2007)

Money isn't an issue with this. It's not just a battery switch, but I'll also need an add a battery kit to keep both charged from the motor. I haven't ran 2 batteries in a small boat in well over a decade and really don't see the need most of the time. If the battery doesn't have enough juice to jump the motor, then you can still easily pull start them. 

The reason I'm running in parallel is just run time for the trolling motor. 100amp/hrs is not enough for the Ipilot. I've read reports that switching batteries while using the ipilot, or running it with a lower charge can also damage them, so this would eliminate any issues there. I actually got the idea off of a few other forums where the big boats guys are running this way, and keeping a Lithium ion jump pack as an emergency backup. I already have a small jump pack that can easily jump my truck that will be kept on the boat.

I'm not super opposed to a 1-2-both switch, I just don't know why I would be doing it that way.


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## verystrange (Oct 6, 2017)

Firecat,
This is exactly what I Have. 2 group 27s with a 12v 55lb ipilot on my dolphin super skiff. One in the bow, one by the motor, connected with 2ga wire under the gunnel. Motor charges both batteries while under power. Only ran trolling motor to point that motor wouldnt start once, and it was hours of run time on TM. Keep a small lithium jump box with you and forget about it.


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## firecat1981 (Nov 27, 2007)

Thanks VS. Unless someone comes up with a compelling reason not to go this way that's the plan. I just think I might go with the group 24's to shed some weight.


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## Gatorgrizz27 (Apr 4, 2015)

Look at running a pair of 6v golf cart batteries in series to get your 12v. I’ve got a set in my tool trailer and everything I’ve seen claims they have a far longer life than other deep cycles. Costco has Interstates for $80 each and you’ll have 210 ah capacity and 383 reserve capacity.

If you run the slightly larger, more expensive ones you can get an insane amount. The only reason I think they aren’t more popular in skiffs is most guys who run all day need 24v.


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## Vertigo (Jun 3, 2012)

The only reason to have two batteries and a switch is if you have a motor you can't pull start. If you need more run time for your trolling motor, just get a bigger deep cycle battery. I wouldn't run my outboard and my trolling motor from the same battery in any case, and I wouldn't rely on my outboard to keep my trolling motor charged. 

The advantage of running two 6 volts in series is that for batteries (6 and 12) with equivalent total weight of lead, two 6 volts (each at half the weight of a 12) will be easier to haul around than one 12 volt. OTOH, they make 6 volt batteries the same size/weight as a 12 volt. In that case the weight to haul around will be double, but because the 6 volt batteries have thicker plates, they will take a lot more cycles. Since weight is usually a consideration in a skiff, the only advantage to lighter 6 batteries in series is portability, but that then comes with the complication of more wiring, more battery mounts, more lugs and fittings to cause problems.

There are many battery solutions depending on the boat and it's usage:

If you're a minimalist, you don't need a battery. Just pull start and navigate by the stars.
If you always pull start, you just need a small 12 volt to run electronics.
If you can pull start in an emergency, you need a small 12 volt starting battery and a TM battery on its own circuit.
If you can't pull start , you need two 12 volt batteries and a switch plus a TM battery on its own circuit.
Of course if you pole instead of troll, you don't need a TM battery in any case.
The list goes on....


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## firecat1981 (Nov 27, 2007)

If your not using your motor to help charge your trolling motor battery when running to different spots then how do you fish all day? With the ipilot drawing heavier then most TM's a group 27 might get you 3 hours, maybe? Many have said I wouldn't.... but haven't really elaborated on why? Why is it better to burn down a battery dead, then switch, rather then use 2 batteries down to half load? If it's just about having a reserve to start the motor then the jump pack takes care of that.

6v batteries are interesting, but they don't rate the golf cart batteries for cranking amps the same. I'll check them out more before I buy a set.


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## tjtfishon (Feb 9, 2016)

I put a 75ah Lithium battery in mine mostly due to fitment issues in the hatch it needed to go into....I could have used a sealed battery on it's side, but since that was three times as much already than a flooded battery I decided to spend even more to shed the weight for LI. I did a lot of reading and research on them and while there is a lot of hype and marketing BS out there, I was convinced that a the lithium technology does effectively give you nearly twice the capacity as the similar rated flooded or AGM battery.


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## tjtfishon (Feb 9, 2016)

firecat1981 said:


> With the ipilot drawing heavier then most TM's a group 27 might get you 3 hours, maybe? .


Keep in mind that is 3 hours at full speed and I don't do a whole lot of trolling at full speed. Using spot lock actually puts very little load on the system...I don't see a problem for most skiffs in using a group 27 battery all day.


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## Edfish (Jan 4, 2013)

tjtfishon said:


> I put a 75ah Lithium battery in mine mostly due to fitment issues in the hatch it needed to go into....I could have used a sealed battery on it's side, but since that was three times as much already than a flooded battery I decided to spend even more to shed the weight for LI. I did a lot of reading and research on them and while there is a lot of hype and marketing BS out there, I was convinced that a the lithium technology does effectively give you nearly twice the capacity as the similar rated flooded or AGM battery.


Quick derail-- tjtfishon, what LI battery did you go with?

Quick but not necessarily useful on topic: Firecat, I just picked up a Duracell grp 27 agm from Sam's club for $160. I plan on running a 55 iplot on a panga marine 18. I'll let you know how it does--I'm assuming I wouldn't make it a full day with heavy TM use, especially if going hard against wind, tide, or both. So on planned long days I'll probably have a "back up" TM battery in the stern (or bow, depending on where I need weight to be/not be). I plan on not wiring in a switch, just moving battery and direct wire TM leads--this decision being made more for sake of simplicity and fewer connections between TM and battery. The outboard will have a dedicated starter battery regardless. I feel like this system will give me the flexibility to go 1 starter/1 deep cycle on short & simple days, and 1 starter/2 deep cycle on days when I think I'll spend 8-10 hrs on the water. **note** I'm very far from an expert at batteries or really any to do with boats, so this is just saying what I'll do, not saying what I think you should do. I was happy with that Sam's club price for the agm though.


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## tjtfishon (Feb 9, 2016)

Edfish said:


> Quick derail-- tjtfishon, what LI battery did you go with?


I got this one https://www.lithiumiontechnologies.com/ which are built in the same Chinese factory as this one https://greenlifebattery.com/ 

After doing a lot of research I was convinced that the Lithium Batteries were close enough to the same lifetime cost as lead/chemical batteries, but had over 50% less weight and 100% more capacity in the same/similar size package. The higher up front cost was really the only thing I could find as a "con" in the pro/con decision.


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## Vertigo (Jun 3, 2012)

Using the same circuit for starting, electronics and trolling motor can lead to problems with electrical interference on things like your chartplotter/fishfinder and VHF while the trolling motor is running. Starting and running a trolling motor from the same circuit will one day lead to not enough capacity to start the outboard....it happens. It's just a good idea to run two separate circuits. A jumper pack is nice, but costs about the same as another battery and is more hassle to deal with and keep charged.


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## tjtfishon (Feb 9, 2016)

Vertigo said:


> A jumper pack is nice, but costs about the same as another battery and is more hassle to deal with and keep charged.


A lithium jump pack is small, lightweight and can be used as battery extenders for phones and other small battery devices. I take mine out every 6 months or so and it has always had a nearly full charge after sitting in the hatch for 6 months. Even with two batteries on board, I wouldn't leave the ramp without one. 

BTW, the only 2 times I have had to use it were to help someone else with a jump. Pretty sure they bought one after that.


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## firecat1981 (Nov 27, 2007)

tjtfishon said:


> Keep in mind that is 3 hours at full speed and I don't do a whole lot of trolling at full speed. Using spot lock actually puts very little load on the system...I don't see a problem for most skiffs in using a group 27 battery all day.


I'm just going off of my current setup. With a 45lbs minn kota I can get about 2.5 hours running in heavy current on a group 27. The ipilot uses more power for the GPS function, but it's a variable speed motor instead of a 5-speed, so it might be more efficient overall.


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## EvanHammer (Aug 14, 2015)

firecat1981 said:


> I'm just going off of my current setup. With a 45lbs minn kota I can get about 2.5 hours running in heavy current on a group 27. The ipilot uses more power for the GPS function, but it's a variable speed motor instead of a 5-speed, so it might be more efficient overall.


I have an 88aH gel battery running my iPilot 55 - I bought a big battery for tarpon fishing off the beach but in most fishing I could go 3 days without charging it. I don't think the iPilot runs the battery down all that quickly in my experience.


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## EvanHammer (Aug 14, 2015)

tjtfishon said:


> I got this one https://www.lithiumiontechnologies.com/ which are built in the same Chinese factory as this one https://greenlifebattery.com/
> 
> After doing a lot of research I was convinced that the Lithium Batteries were close enough to the same lifetime cost as lead/chemical batteries, but had over 50% less weight and 100% more capacity in the same/similar size package. The higher up front cost was really the only thing I could find as a "con" in the pro/con decision.


Which specific battery and charger did you buy? I've been thinking about switching to lithium ion to save weight and will probably pull the trigger if you have had a good experience.


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## JMZ400 (Aug 30, 2015)

FWIW when I installed my 12v 55lb thrust ipilot, I had planned on going lead acid and just wiring it up in the rear of the boat where it wouldn't get beat to death. Then I stared pricing wire and realized that for the price of the wire in the proper gauge to run that distance, I could buy an AGM and mount it up front. I ended up getting the Duracell Group 31 AGM from Sam's. So far I've been out twice with it and neither day ran it down. I trolled all day.


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## topnative2 (Feb 22, 2009)

https://www.bluesea.com/products/category/35/Automatic_Charging_Relays


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## tjtfishon (Feb 9, 2016)

EvanHammer said:


> Which specific battery and charger did you buy? I've been thinking about switching to lithium ion to save weight and will probably pull the trigger if you have had a good experience.


I got the 75, but the 50 would have probably been fine. I use a NOCO Genius 3500 which has a Lithium setting, but you can use any charger that is suitable for AGM batteries. I've had it onboard for about 5 months and I would buy it again (so far). The weight savings is incredible and the fact that you get full voltage output basically until the battery is low enough to turn itself off is a nice change from the sluggish output of a lead acid battery after a day of running around with the TM.


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## EvanHammer (Aug 14, 2015)

tjtfishon said:


> I got the 75, but the 50 would have probably been fine. I use a NOCO Genius 3500 which has a Lithium setting, but you can use any charger that is suitable for AGM batteries. I've had it onboard for about 5 months and I would buy it again (so far). The weight savings is incredible and the fact that you get full voltage output basically until the battery is low enough to turn itself off is a nice change from the sluggish output of a lead acid battery after a day of running around with the TM.


Thanks


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## DBStoots (Jul 9, 2011)

I have two Optima Bluetop 34M's up front for the TM and one in the console as a starting/house battery. This thread got me wondering how old they are as my skiff is a 2013. Turns out two were made in 2012 and one was made in 2013! I put all three on trickle charge in the garage as soon as the boat is clean and dry. Wonder if I am pushing my luck and should consider replacing them? Since installing the Simrad EVO3, I have gotten low voltage warnings if the machine is on a long time without the motor running.


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## sjrobin (Jul 13, 2015)

Vertigo said:


> Using the same circuit for starting, electronics and trolling motor can lead to problems with electrical interference on things like your chartplotter/fishfinder and VHF while the trolling motor is running. Starting and running a trolling motor from the same circuit will one day lead to not enough capacity to start the outboard....it happens. It's just a good idea to run two separate circuits. A jumper pack is nice, but costs about the same as another battery and is more hassle to deal with and keep charged.


Truth


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## sjrobin (Jul 13, 2015)

DBStoots said:


> I have two Optima Bluetop 34M's up front for the TM and one in the console as a starting/house battery. This thread got me wondering how old they are as my skiff is a 2013. Turns out two were made in 2012 and one was made in 2013! I put all three on trickle charge in the garage as soon as the boat is clean and dry. Wonder if I am pushing my luck and should consider replacing them? Since installing the Simrad EVO3, I have gotten low voltage warnings if the machine is on a long time without the motor running.


I would replace the five year old group 34 Optima starting battery based on the low voltage alarm. From my experience five years is good for an Optima Blue group 34. My current starting Optima is a 2015 model. If you have NMEA 2000 cable on your Simrad, the NMEA draws a little current even when the Simrad is off. Don't forget to turn your power switch off when not using the skiff.


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## State fish rob (Jan 25, 2017)

Battery jump boxes have been a life saver no doubt. Size matters. 5 size 27 in bay boat going on 6 years. 36 v ipilot 2 on switch Keep water topped off , keep them charged every couple months I ve not had one let down. Lot of work to keep from having to replace them No telling what ive spent in the last 20 yrs on batteries. Ive killed them every way known to man and then some


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## Salt of the Water (Feb 26, 2018)

Edfish said:


> Quick derail-- tjtfishon, what LI battery did you go with?
> 
> Quick but not necessarily useful on topic: Firecat, I just picked up a Duracell grp 27 agm from Sam's club for $160. I plan on running a 55 iplot on a panga marine 18. I'll let you know how it does--I'm assuming I wouldn't make it a full day with heavy TM use, especially if going hard against wind, tide, or both. So on planned long days I'll probably have a "back up" TM battery in the stern (or bow, depending on where I need weight to be/not be).


I'm using two Duracell 27 agms from Sams to run a 24v 80lb ipilot on a 19 panga. I can pretty much run a full weekend with normal use (high/medium speeds between spots, slow speed while fishing) and not have to charge. My motor doesn't charge my TM batteries. I think you might be able to get a full day out of your rig, unless the 55lb just can't keep up with the wind load on your hull. The AGM gives you a better discharge profile. Regular lead acids only like to bee cycled to about 50%. the AGM can handle discharging much closer to 0%.


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