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Old 02-15-2021, 08:43 PM   #1
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New battery technology ?

My son's 44' Kelly Peterson needs it's 3 bank 8 D batteries replaced. What are the forum's thoughts about what new technology in batteries might offer as an alternative to just replacing what has been there since forever?
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Old 02-16-2021, 08:16 AM   #2
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There are LOTS of threads on batteries, so in the meantime you should search for those and digest away.

Partly I say that because your question as it stands is so open ended... it's almost like the "piece of string" question...

What for? How organized (start versus house banks)? What end voltage? What capacity is required? What space is available (for alternatives)? And so forth...

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Old 02-16-2021, 08:34 AM   #3
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Chris is right on with the questions. Additional information could be useful. In general terms, I've heard a number of my marina neighbors replacing old 8Ds with new AGM Group 31 batteries.
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Old 02-16-2021, 08:49 AM   #4
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Weight is usually not a consideration in boats, space is and lithium batteries take the same space as FLAs or AGMs. There are other advantages to lithiums, but not enough to make their price premium worthwhile IMO.

The cheapest and maybe the most effective way is to replace your three 8Ds with 6 golf cart batteries wired in series/parallel. That will give you 660 amp hours of nominal capacity. The only real downside is checking the water levels and adding periodically- 3-4 times a year. They cost $100ish each at Batteries Plus or Costco.

If it is too much trouble to check water levels then replace the 8Ds with six 12V, Group 31 AGMs. These can be bought as cheap as $180 each on Amazon for 100 Ah Windy Nation batteries, $200+ for Renogy and several hundred for premium brands.

Both the GCs and the G31 AGMs will fit in the same space as the 8Ds.

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Old 02-16-2021, 09:31 AM   #5
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Originally Posted by JohnEasley View Post
Chris is right on with the questions. Additional information could be useful. In general terms, I've heard a number of my marina neighbors replacing old 8Ds with new AGM Group 31 batteries.
I replaced my 8Ds 7 seasons ago with AGM 8Ds as it was an easy plug in. That was the last 8D I will use.
Like others indicated GC or GP31s are an easy replacement with a few more cables. AGMs are good at both deep cycle and starting if it is a mixed use bank. Many now spec both AHs and CCA so its easy to compare and decide which is best. Both East Penn (Sams Club Duracell) and Trojan have told me no deep cycle or start performace difference between GC and GP31 if AGMs... very different in FLA.
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Old 02-16-2021, 09:35 AM   #6
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I'm with you David. There seems to be a blind rush to lithium batteries, the relevant benefit of which escapes me except in very limited circumstances. Space, though, is one of them because a similar size bank can be had using less space. Longevity? Who cares. A FLA bank generally lasts 6-8 years. Who among us replacing a battery bank with lithium will even still own that boat in eight years? Pretty much, the installer of lithium batteries will never see a cost benefit, but the next owner may.
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Weight is usually not a consideration in boats, space is and lithium batteries take the same space as FLAs or AGMs. There are other advantages to lithiums, but not enough to make their price premium worthwhile IMO.

The cheapest and maybe the most effective way is to replace your three 8Ds with 6 golf cart batteries wired in series/parallel. That will give you 660 amp hours of nominal capacity. The only real downside is checking the water levels and adding periodically- 3-4 times a year. They cost $100ish each at Batteries Plus or Costco.

If it is too much trouble to check water levels then replace the 8Ds with six 12V, Group 31 AGMs. These can be bought as cheap as $180 each on Amazon for 100 Ah Windy Nation batteries, $200+ for Renogy and several hundred for premium brands.

Both the GCs and the G31 AGMs will fit in the same space as the 8Ds.

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Old 02-16-2021, 09:41 AM   #7
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Weight is usually not a consideration in boats, space is and lithium batteries take the same space as FLAs or AGMs.

David
This is not true when comparing the same useable Ah from the battery bank. Lithiums, for a given useable Ah capacity, take up a smaller VOLUMETRIC space than FLA or AGM.

An example comparison is below.

As you state, the weight difference is drastic. Also there can be up to a 5x increase in cycle life with lithium.
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LithiumCompareExample.jpg  
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Old 02-16-2021, 11:07 AM   #8
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Yes I agree, on the basis of usable amp hours, Lithium batteries take up less space than AGMs or FLAs if you hold to the 50% usable percentage for the latter.

I am becoming a little less wedded to the 50% rule of thumb. Over a 6+ year life if you run an AGM or FLA down to 20% AND IMMEDIATELY RECHARGE IT THE NEXT DAY, I don't think doing that occasionally will be noticed in reduced life. But leaving them discharged for long will kill them due to sulfation.

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Old 02-16-2021, 11:23 AM   #9
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Yes I agree, on the basis of usable amp hours, Lithium batteries take up less space than AGMs or FLAs if you hold to the 50% usable percentage for the latter.

I am becoming a little less wedded to the 50% rule of thumb. Over a 6+ year life if you run an AGM or FLA down to 20% AND IMMEDIATELY RECHARGE IT THE NEXT DAY, I don't think doing that occasionally will be noticed in reduced life. But leaving them discharged for long will kill them due to sulfation.

David
Exactly!
The 50% DOD is often repeated and has become gospel. IMO it is a myth. 70%-80% DOD is a more realistic cut off... especially if that use is occasional vs daily 365. If a full timer and at anchor most of the time the whole system design and economics likely a different story.
Batteries are a source of AHs and within about 5%-10% are capable of delivering the (close to) same AH whether you draw to 50% or 75% DOD.
I have posted a more complete analysis in other threads and can repeat if there is interest.
Trojan also confirms the higher DOD as good practice.
I won't argue the expected life for Li as I think it is still too early to have good data. How many here have had a Li bank / system in place for 15-20 yrs to clearly show they have done better than break even on $/AH over batty life?
I'm not interested as I won't be boating when / if I could reach the break even... heck I may not be alive by then?
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Old 02-16-2021, 11:31 AM   #10
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Exactly!
The 50% DOD is often repeated and has become gospel. IMO it is a myth. 70%-80% DOD is a more realistic cut off... especially if that use is occasional vs daily 365. If a full timer and at anchor most of the time the whole system design and economics likely a different story.
Batteries are a source of AHs and within about 5%-10% are capable of delivering the (close to) same AH whether you draw to 50% or 75% DOD.
I have posted a more complete analysis in other threads and can repeat if there is interest.
Trojan also confirms the higher DOD as good practice.
I won't argue the expected life for Li as I think it is still too early to have good data. How many here have had a Li bank / system in place for 15-20 yrs to clearly show they have done better than break even on $/AH over batty life?
I'm not interested as I won't be boating when / if I could reach the break even... heck I may not be alive by then?
It is not a myth - there is a direct correlation between DOD and cycle life of the battery. Somebody decided that 50% was a good compromise between cycle life and useable energy and it stuck.



Lifeline battery effect of DOD on cycle life - Source: https://shop.pkys.com/
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Old 02-16-2021, 11:42 AM   #11
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50% is a good design goal partly based on the total lifetime power compromise, but also because it leaves some headroom in case you have to draw them down further every once in a while.

As far as lithium, the biggest thing that makes me consider it is weight. If I can fit more batteries in the same weight envelope, I can add capacity without worrying about trim, costing speed, etc. But at the moment, the price is too high for me to feel it worth making the jump from AGMs.
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Old 02-16-2021, 11:53 AM   #12
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It is not a myth - there is a direct correlation between DOD and cycle life of the battery. Somebody decided that 50% was a good compromise between cycle life and useable energy and it stuck.



Lifeline battery effect of DOD on cycle life - Source: https://shop.pkys.com/
But think about it...
30% DOD = about 1700- 1800 cycles and half the AHs as 60% DOD and about 800 cycles.
To half the DOD you need to recharge twice as often and that uses up the "extra" life everyone refers to... so no / little real gain.
Only other way is to double the size of the batty bank and if you compare $/AH delivered its still a wash.
# cycles doesny mean the batty lasts longer just more fewer AH cycles vs fewer larger AH cycles.

Attached is a more complete analysis including $/AH and Trojan recommendations.
Attached Thumbnails
USB Batty Life.jpg  
Attached Files
File Type: pdf Useful Battery Life Analysis 50% DOD Myth Busting Rev 1.pdf (345.9 KB, 21 views)
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Old 02-16-2021, 11:57 AM   #13
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But think about it...
30% DOD = about 1700- 1800 cycles and half the AHs as 60% DOD and about 800 cycles.
To half the DOD you need to recharge twice as often and that uses up the "extra" life everyone refers to... so no / little real gain.
Only other way is to double the size of the batty bank and if you compare $/AH delivered its still a wash.
# cycles doesny mean the batty lasts longer just more fewer AH cycles vs fewer larger AH cycles.
Depending on the batteries, the graph is often not linear. So once you get down to the deeper discharges, the cycle count drops off fast enough that you'll get less total AH delivered over the life of the batteries. Plus, as you drain them further, the voltage can start to dip pretty low if you have any large power draws relative to the size of the battery bank.
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Old 02-16-2021, 12:17 PM   #14
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LFP batteries will deliver more AH/$ over their life than LA, but if you aren't planning to keep the boat for about 10 years you will not benefit. Even LFP batteries degrade with calendar time, so 15-20 years sometimes tossed out is not likely. However so far unmentioned in this thread is the real advantage of LFP - much faster recharge time and indifference to operation at partial states of charge. If the genset is on most of the day for cooking or AC then that doesn't matter, but for some it is a very big benefit. Depends on how you use and operate your boat.
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Old 02-16-2021, 12:24 PM   #15
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Depending on the batteries, the graph is often not linear. So once you get down to the deeper discharges, the cycle count drops off fast enough that you'll get less total AH delivered over the life of the batteries. Plus, as you drain them further, the voltage can start to dip pretty low if you have any large power draws relative to the size of the battery bank.
I won't argue that is absolutely linear but the loss is small until you get closer to 100% DOD that is recommended.
MY PRIMARY ARGUMENT IS THAT IT CHANGES LITTLE AT 50%. IF THE MYTH WERE TRUE THERE WOULD BE A SHARP INFLECTION POINT ABOVE 50% DOD.
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Old 02-16-2021, 12:33 PM   #16
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LFP batteries will deliver more AH/$ over their life than LA, but if you aren't planning to keep the boat for about 10 years you will not benefit. Even LFP batteries degrade with calendar time, so 15-20 years sometimes tossed out is not likely. However so far unmentioned in this thread is the real advantage of LFP - much faster recharge time and indifference to operation at partial states of charge. If the genset is on most of the day for cooking or AC then that doesn't matter, but for some it is a very big benefit. Depends on how you use and operate your boat.
LFP batteries (and associated system to take advantage... new larger chargers, alternators, etc) will take much more than 10 yrs to break even.
I am using a rough guide of $1/ AH FLA, $2/AH AGM and $5-$10/ AH LFP.
My AGMs are 7 yrs and still strong... Im expecting 8-10 yrs from my AGMs but admit my seasons are shorter than some.. doubt LFP will be as good in 15-20 yrs to break even noless come out ahead?
Just my thoughts and not knocking those that feel LFP works for them. I'm not saying it makes no sense but rather do an honest and complete analysis for your situation and use.
As prices come down the economics will improve similar to the way AGMs have improved.
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Old 02-16-2021, 12:40 PM   #17
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It is not a myth - there is a direct correlation between DOD and cycle life of the battery. Somebody decided that 50% was a good compromise between cycle life and useable energy and it stuck.



Lifeline battery effect of DOD on cycle life - Source: https://shop.pkys.com/
Interesting discussion.

If you took the 500 cycle estimated lifespan at what 80-90% DOD and extrapolated that over time, how long would a FLA bank last for the average TF member?

Even for a full time cruiser how many years are we really talking about? I do not know other folks cruising habits but I almost never just sit at an anchorage for day upon day and never move. We pull into an anchorage spend the evening, maybe the next day but after that we are going somewhere. That going somewhere time is battery recharge time. Then we have other things that we need to run the generator for anyway. Things like making water for example, doing laundry, cooking. This generator run time is again battery recharge time.

I would argue that for most cruisers who maintain their FLA banks regularly they get several years or even a decade of useful life from their bank.
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Old 02-16-2021, 12:42 PM   #18
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Boaters love to discuss and spend money on batteries.

Your son's batteries have been there "forever" so why change to something more expensive?

Pay some kids to hump the 8Ds and be done with "forever"
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Old 02-16-2021, 01:03 PM   #19
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Interesting discussion.

If you took the 500 cycle estimated lifespan at what 80-90% DOD and extrapolated that over time, how long would a FLA bank last for the average TF member?

Even for a full time cruiser how many years are we really talking about? I do not know other folks cruising habits but I almost never just sit at an anchorage for day upon day and never move. We pull into an anchorage spend the evening, maybe the next day but after that we are going somewhere. That going somewhere time is battery recharge time. Then we have other things that we need to run the generator for anyway. Things like making water for example, doing laundry, cooking. This generator run time is again battery recharge time.

I would argue that for most cruisers who maintain their FLA banks regularly they get several years or even a decade of useful life.
No argument. But boaters are hobbyists. Trying new things without too many reservations is part of our nature.

Regarding the OP's question, I'm cheap sometimes. But paying some young strong back a $50 bill to replace my two 8D FLA starts every 4-5 years is worth it.
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Old 02-16-2021, 01:15 PM   #20
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There are a couple of other advantages to Lithiums in respect to charge rate, if you wish to reduce your generator run time to charge batteries then Lithiums can help achieve that. To take full advantage of that you need other upgraded equipment as well, and it's only an advantage in some situations, it depends on your usage patterns. Carbon foam AGMs can also provide this type of advantage.

The other one is reduced voltage sag under load. Lithiums hold their voltage better during discharge than lead acid batteries do which can be better for your equipment. Lithiums hold their voltage quite a bit higher than lead acid until they are almost completely discharged, at which point they fall rapidly.

A cost benefit analysis is a complex question that is driven by a bunch of factors including how long you will use the system, how you use the system, and how often you use it to its full abilities. If you mainly are at a marina plugged into shore power, I see little to no advantage. If you want to have systems capable of extended 'on the hook periods', Lithiums with appropriate support systems can have an advantage.
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