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 8D’s with provide house power and of course for starting the motors. 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.

Thanks!

I don’t like 8Ds for a couple of reasons. First they are really heavy. Second they don’t 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.

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.

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.

David

Is there a battery half the footprint of 8Ds that will fit two in the same box sized for one 8D?

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.

bayview said:

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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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.

David

Longo said:

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.

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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...)

bayview said:

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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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.

-Chris

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.

bayview said:

Is there a battery half the footprint of 8Ds that will fit two in the same box sized for one 8D?

Click to expand...

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.

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.

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.

rsn48 said:

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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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 User’s 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

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.

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

Golf carts don't float

Comodave said:

I don’t like 8Ds for a couple of reasons. First they are really heavy. Second they don’t 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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https://www.fisheriessupply.com/lifeline-battery-12v-8d-agm-deep-cycle-batteries

DavidM said:

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

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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.

Comodave said:

I don’t like 8Ds for a couple of reasons. First they are really heavy.

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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 .

DavidM said:

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

Click to expand...

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.

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.

fgarriso said:

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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When is the last time you moved the lead ballast in your keel? But on the other hand you do actually have to lift batteries in and out of the boat. And lifting the 8Ds are really difficult.

Longo said:

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 8D’s with provide house power and of course for starting the motors. 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.



Thanks!

Click to expand...

We replaced the 8Ds in our Pilot 34 with dual purpose AGM G31s three years ago and the Protech 1240 charger has had no issues keeping them charged. The 8Ds are difficult to move and two G31s fit in the footprint of one 8D. We were lucky enough to have purchased them on sale at west marine.

Dual purpose batteries are generally not the "best" choice for house (deep cycle) use. Deeply discharging them can lead to early failure.

Bacchus has provided some good info. Best "value" for your money (least money spent per AHr) are flooded lead acid deep cycle batteries for a deep cycle house bank. However, there are disadvantages. They must be regularly recharged to 100% FULL charge (at least every few days). This takes many hours to put in the last portion. Total recharge time can run over 5 hours. Many boaters murder their batteries by not fully recharging them often enough (operate at a partial state of charge). Firefly excel at PSOC operation. Lead acid require maintenance (watering), and they can "off gas".
AGM's make sense if access for watering is a problem. They are actually even a bit more sensitive to PSOC operation than flooded lead acid, so failure to fully recharge on a regular basis could create conditions of an early demise even more so than for flooded lead acid.
I agree about the 8D's being way too heavy. I have 2 currently. When they need replacement, I will be looking for alternatives.

IF the boat was large enough to hold many heavy batts , by the chart shown installing enough batt capacity and only discharging 10% would make the most sense long term.


Looks like 5,000 discharges would serve most folks.

I’ve seen this mentioned more than once- replacing two Group 31 in the footprint of an 8D. I don’t see how they fit. Full disclosure: I’m not good at puzzles and might not have had enough coffee yet.

8D: 20-3/4” x 11”

GR 31: 13” x 6-3/4”

firehoser75 said:

Dual purpose batteries are generally not the "best" choice for house (deep cycle) use. Deeply discharging them can lead to early failure.

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Yeah, our banks of dual-purpose G31 AGMs -- used for both starting and house loads -- only lasted about 12 seasons each.

-Chris

Chris, with much respect, a single person's experience is not relevant. Useage patterns are so very different one from another. Sure, dual-purpose batteries can last a long time but for any boater who is a heavy overnight user of juice, day after day, depleting the bank to 50% over and over, the science of batteries is definitive, dual use batteries are not as good to purpose as flooded lead acid, or deep cycle AGM, or, lithium. They just aren't. They work for you and that's good but they are not a good choice for others.

ranger42c said:

Yeah, our banks of dual-purpose G31 AGMs -- used for both starting and house loads -- only lasted about 12 seasons each.

-Chris

Click to expand...

firehoser75 said:

Dual purpose batteries are generally not the "best" choice for house (deep cycle) use. Deeply discharging them can lead to early failure.

Click to expand...

ranger42c said:

Yeah, our banks of dual-purpose G31 AGMs -- used for both starting and house loads -- only lasted about 12 seasons each.

Click to expand...

IMO and what I have tried to convey...

What is often, but not always, missing in most of the batty discussions is the differentiation between FLA and AGM.
In general, generalizations about starting vs deep cycle can't be objective without specifying the type...

catalinajack said:

Chris, with much respect, a single person's experience is not relevant. Useage patterns are so very different one from another. Sure, dual-purpose batteries can last a long time but for any boater who is a heavy overnight user of juice, day after day, depleting the bank to 50% over and over, the science of batteries is definitive, dual use batteries are not as good to purpose as flooded lead acid, or deep cycle AGM, or, lithium. They just aren't. They work for you and that's good but they are not a good choice for others.

Click to expand...

Bacchus said:

IMO and what I have tried to convey...

What is often, but not always, missing in most of the batty discussions is the differentiation between FLA and AGM.
In general, generalizations about starting vs deep cycle can't be objective without specifying the type...

Click to expand...

Yep. And yep. I was only attempting to temper the earlier generalization.

Especially because many boats are set up with no separate house bank... so batteries are actually doing dual-purpose functions.

Didn't at mean to seem combative, or to indicate our experience is representative.

-Chris

ranger42c
No offense taken, in fact I believe you are not alone or way beyond whats possible with proper care.
Our AGM 8Ds that have served house & start have gone 7 seasons and still going strong. I have recently moved start to my thruster bank more to have a pure house and in my case all battys are AGM 8Ds.
I'm curious what brand your GP31s are as my plan replacing my 8Ds is to go GP31s.
I had about 10 AGM UPS battys that were "discarded" as end of useful life. I used several for many years. Kept a few on maintainers for about 10 years and finally gave away the last 2 that arecworking fine in a friends fishing boat. So for me, nothing but good experience w AGMs and no disappointments.
Take care of them as recommended and they will take care of you.