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Old 01-03-2021, 03:41 PM   #1
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New battery purchase

Hello all,

Looking to replace the batteries on my boat - Albin 37 with two Volvo TAMD40B (165 horse 6 cylinder diesels). Boat came with and currently has two 8Dís with provide house power and of course for starting the motors. Does anyone have any recommendations which are good replacements - do i need 8Dís or can i go with 4Ds for a little less weight and cost.

Thanks!
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Old 01-03-2021, 03:50 PM   #2
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I donít like 8Ds for a couple of reasons. First they are really heavy. Second they donít make a true deep cycle. I would recommend that you make 2 banks. One for starting and one for house bank. Get a good starting battery and then go with true deep cycle battery for house bank like 6 volt Golf Cart batteries. It makes your setup more complicated but it will serve as a good starting system and a good deep cycle system.
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Old 01-03-2021, 03:52 PM   #3
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There are plenty of threads on this, the space and mounting facilities you have may dictate different but: nobody in their right mind puts 8D in to a small trawler anymore. I have 4D and am about to replace them as well. If you can, go with 6V golf cart footprint batteries. These are lighter to move and easier to pack. They are available anywhere for replacement, and are available in 3 heights depending on space and needs - the original 200AH, taller 300AH and L16 sized 400AH. For example in Lifeline AGM the GPL-4CT, -6CT, or -L16T offerings.
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Old 01-03-2021, 04:28 PM   #4
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I wrote an article on this topic which you can find in the Library of this forum- click the icon in the upper right corner of this page.

A good Group 31 battery can easily start that engine and will be half the weight of an 8D.

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Old 01-03-2021, 04:39 PM   #5
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Is there a battery half the footprint of 8Ds that will fit two in the same box sized for one 8D?
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Old 01-03-2021, 05:11 PM   #6
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My Mainship 34HT has a pair of AGM 8Ds for house / start and a 3rd AGM 8D for thrusters.
I swore the only time I will consider handling an 8D again is to remove the current ones.
I decided to separate my start from the house and tie in with the thrusters leaving a pure house. Previously I was thinking a pair of GP31s for thruster / start and 4 GCs for house. For AGM both East Penn and Trojan confirmed Gp31s and GCs both perform equally well in deep cycle and start applications.
My current plan is to replace each 8D with 2 GP 31 AGMs 2 for start / thruster and 4 for house.
If using FLA you should be able to fit a pair of GCs for house use and a GP31 for start or put a pair of GCs in place of each existing 8D but wire start to one pair and use the other pair as house. GCs are plenty capable of starting. With a 1-2-all-off switch between the start / house banks it would let you separate them for normal use but combine if / when necessary of desirable.
Others are proponents of just putting in the largest bank possible and using for both start & house. If you have a separate gen & gen batty as a back-up that might be a possibility if not that approach could be dangerous.
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Old 01-03-2021, 05:30 PM   #7
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Quote:
Originally Posted by bayview View Post
Is there a battery half the footprint of 8Ds that will fit two in the same box sized for one 8D?
Yes, for house use two 6V golf cart batteries will fit in the space of one 8D. A Group 31 for starting will fit in place of the other 8D with room to spare. That is exactly what I did with my Mainship Pilot 34.

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Old 01-04-2021, 09:16 AM   #8
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Does anyone have any recommendations which are good replacements - do i need 8D’s or can i go with 4Ds for a little less weight and cost.

I don't even much care for 4Ds. Group 31s are easier for me to shift... Four G31s, some brands, could come close to the same capacity you have with two 8Ds. (I'd been shopping on Lifeline G31 XTs, 125-Ah each...)


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Is there a battery half the footprint of 8Ds that will fit two in the same box sized for one 8D?
Six GC2s will fit in two 8D boxes. That would be approx. 660 Ah capacity, very decent for house bank size... and the 3 pairs would offer sufficient cranking amps to start.

If OPs two 8Ds are combined in a single bank as both house and start for both engines, then 6x GC2s could be nifty. OTOH, if his setup is configured as each 8D for one engine and half the house ... maybe 4x G31s would be simplest. Or maybe in that case and if space is available, 3x G31s for each bank could offer some additional improvement.

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Old 01-04-2021, 09:54 AM   #9
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Your battery choices are 8D, 4D, Group 31, L16, floor sweeper, and golf car. Each type is a standard size as to length, width, and height among all manufacturers. Measure your space and compare to the footprint of whatever battery you are considering.
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Is there a battery half the footprint of 8Ds that will fit two in the same box sized for one 8D?
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Old 01-04-2021, 10:13 AM   #10
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Once you decide on the type of battery, call Pascoe in Maryland for the best price on Rolls batteries. Last summer, the Rolls were as cheap as Trojans, but were 30lbs heavier each in the same size. You are buying lead and lead=capacity.
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Old 01-04-2021, 10:28 AM   #11
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If you don't want / need top of the line battys & associated $$$ I have had great success with Duracells made in US by East Penn and readily available st Sams Club.
I find them about the best $$ / AH / Cycle and IMO a "Best Buy"
They are available in either FLA or AGM and both are very decent battys at attractive $$.
My East Penn AGN 8Ds have served me well for 7 seasons and still going strong - replacements will be Duracell AGM Gp31s or GCs.
No argument you can find "better" battys but I question whether anyone can reach a breakeven when you figure the 1.5X - 2X price of the top of the line.
Just my thinking and nothing against the "better" batty manufacturers.
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Old 01-04-2021, 11:36 AM   #12
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If you overnight much on the hook, you would be better off with AGM batteries. Flooded lead acid batteries should only be discharged to 50 % and usually can only be charged 35 % to 85 % when out and about on your boat, float takes so long. So a way to increase the amount of energy without increasing the amount of batteries is to purchase batteries that can discharge deeper.

Firefly batteries can be discharged down to 20 % and can take a charge much faster than traditional AGM's and FLA. They are the closest battery to lithiums without being lithiums (which require a lithium "system"). They can also withstand many more cycles do they will most likely be the last batteries you buy, they don't sulfate. So the price is more but because of their longevity and the fact you probably will never have to purchase more batteries, over the long run are cheaper, but not cheap to initially purchase.
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Old 01-04-2021, 01:36 PM   #13
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If you overnight much on the hook, you would be better off with AGM batteries. Flooded lead acid batteries should only be discharged to 50 % and usually can only be charged 35 % to 85 % when out and about on your boat, float takes so long. So a way to increase the amount of energy without increasing the amount of batteries is to purchase batteries that can discharge deeper.

Firefly batteries can be discharged down to 20 % and can take a charge much faster than traditional AGM's and FLA. They are the closest battery to lithiums without being lithiums (which require a lithium "system"). They can also withstand many more cycles do they will most likely be the last batteries you buy, they don't sulfate. So the price is more but because of their longevity and the fact you probably will never have to purchase more batteries, over the long run are cheaper, but not cheap to initially purchase.
Not knocking Firefly but the 50% limit for discharge is an oft repeated myth IMO
See the attached for a more detailed reason why and confirmation by Trojan

Note: To reinforce the above I quote the Trojan Battery Co User Guide
https://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf
Maximizing the Performance of Your Trojan Battery
1. Follow all the procedures in this Userís Guide for proper installation, maintenance and storage.
2. Do not discharge your battery to more than 80% depth of discharge.
This safety factor will eliminate the chance of over-discharging and damaging your battery
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Old 01-04-2021, 02:12 PM   #14
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AGM's are available in almost any size/dimension you may want. The quality also varies just as much. Plenty of battery manufacturers over-estimate their Ah capacity, but the weight tells the story.

As WH mentioned, Lead = weight = Ah capacity.
AGM batteries generally put out 3.5Ah/kg. (1.5Ah/pound) although some claim more and deliver less.
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Old 01-04-2021, 03:40 PM   #15
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Don:

Am I reading you right? Are you saying that a plain vanilla GC2 battery will get roughly the same cycles at a DOD of 80% as a Firefly battery will?

Makes some sense as lead sulfate sloughing is the biggest cause of battery failure and that should happen to Firefly's as well.

How about the other Firefly claims like faster charging?

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Old 01-04-2021, 04:15 PM   #16
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Quote:
Originally Posted by Comodave View Post
I donít like 8Ds for a couple of reasons. First they are really heavy. Second they donít make a true deep cycle. I would recommend that you make 2 banks. One for starting and one for house bank. Get a good starting battery and then go with true deep cycle battery for house bank like 6 volt Golf Cart batteries . It makes your setup more complicated but it will serve as a good starting system and a good deep cycle system.


https://www.fisheriessupply.com/life...ycle-batteries
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Old 01-04-2021, 04:17 PM   #17
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Don:

Am I reading you right? Are you saying that a plain vanilla GC2 battery will get roughly the same cycles at a DOD of 80% as a Firefly battery will?

Makes some sense as lead sulfate sloughing is the biggest cause of battery failure and that should happen to Firefly's as well.

How about the other Firefly claims like faster charging?

David
Faster charging requires higher output alternators. Firefly batteries have a charge acceptance rate of about 50% while common lead acid batteries accept about 20%. So, for a 1000ah battery bank a Firefly bank would need 500 amps of alternator charging in order to take advantage of the Firefly's ability to charge faster. Meanwhile those lead acid batteries would accept as much as 200 amps from the alternators. Now, who among us has any more than 200 amps worth of alternators considering the derating that occurs for alternator case temps? So, to me the Firefly battery's ability to accept more amps is pretty much meaningless. Their main advantage is that they can be more deeply discharged but even that is not much of a big deal unless available space for batteries is a limiting factor.

Think about this. A Trojan FLA battery is rated for 800 cycles at 70% discharge. That's 800 nights of really beating up on the batteries. So, ask yourself this. How many overnights do you do each year?

As far as bringing FLA batteries up to 100%, it takes me about five hours of cruising to fully recharge a 932ah bank that has been depleted to 60%. And, as long as FLAs are brought to 100% every few days, they do just fine in terms of battery life.

Firefly battery are rated to last 2 - 3 times that of FLAs at 80% discharge. That would be 2,400 cycles, at most. Eight Group 31s (932ah) would cost $4,344. Eight Trojan T-105s (900ah) would cost about $1,120. Are Firefly batteries more cost effective? Nope.
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Old 01-04-2021, 04:41 PM   #18
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I donít like 8Ds for a couple of reasons. First they are really heavy.
I have 2400 lbs. of lead in the bilge keel for blast. Wat's another 300 lbs. for two more batteries going the effect anyway .
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Old 01-04-2021, 04:47 PM   #19
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Don:

Am I reading you right? Are you saying that a plain vanilla GC2 battery will get roughly the same cycles at a DOD of 80% as a Firefly battery will?

Makes some sense as lead sulfate sloughing is the biggest cause of battery failure and that should happen to Firefly's as well.

How about the other Firefly claims like faster charging?

David
David
No thats not what I'm saying. One would have to have cycle life charts from specific battys to compare that. From what I've read mfgrs do not do cycle lIfe testing consistently so really comparing fruit salad.
My point I am trying to make in the attached file is that when folks claim that if you draw a batty down below 50% DOD is is somehow damaged or significantly shortens its life.

None of the cycle life charts I have ever seen shows a precipitous drop in cycles when drawn down below 50%. Therefore even the batty mfg do not promote such a notion and Trojan confirms it by recommending a 80% DOD as a reasonable limit

If you think of a batty as an energy storage device a more meaningful measure of a battery's useful life is the total AH it is capable of delivering over its life. The comparison is more meaningful when you consider the economics by calculating $/total AH delivered.

That seems (to me) much more meaningful that measuring a battery in terms of calendar yrs or cycles as both will vary greatly based on how they are used.
Sort of similar to measuring an auto life only in years or # of trips. That varies too much with how it is used and total miles is a much more reasonable and more often used measure of an auto "useful life"

Some claim it is "better" to oversize a batty bank and only go to 20% DOD as they will last much longer... but that ignores the greater initial investment.

My contention is that there are much smaller differences that most espouse if you consider the initial cost and total AH delivered over that batty bank life.
I'm not a Firefly user nor have I researched them so can't reasonably endorse or knock them. I would welcome a real apples / apples comparison of $ / AH delivered over its life. Im skeptical that the higher end battys can breakeven or beat a good mid level batty on that $/AH basis.
Attached Thumbnails
Batty Life vs DOD.jpg  
Attached Files
File Type: pdf Useful Battery Life Analysis 50% DOD Myth Busting Rev 1.pdf (345.9 KB, 12 views)
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Old 01-04-2021, 05:13 PM   #20
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Firefly and other good AGM batteries have similar charge acceptance (and better than typical flooded). But the real advantage of Firefly carbon foam batteries is their resistance to sulfation when run for extended periods at a partial state of charge. For this you pay a very premium price. Their niche seems to be disappearing as LFP batteries get cheaper.
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