I'm setting up a new 24 volt house bank. I was told that two 12 volt batteries hooked in series to make 24 volts, will last twice as long as one 24 volt battery. Something to do with a work formula. Can anyone confirm this? Thanks
Two batteries vs one for longevity
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Generally that statement is not true. Hooked in series, voltages add, but AH capacity does not. So one 100 AH 24V battery has the same capacity as two 100 AH 12V batteries hooked in series to make 24V. Hooked in parallel, AH capacity adds, but voltage does not. There is really no free lunch in batteries - however you do it, it costs about the same, weighs about the same, and takes about the same volume, unless you change to a radically different chemistry like Lithium.
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Mac2
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I should have clarified better. I meant the overall life of the battery vs the AH of the battery. i.e. if you use two battery banks identically, the two 12 volt batteries in series will last twice as long (lifespan) as the single 24 volt battery.
tiltrider1
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Assuming all thing equal this is a false statement. A 24v battery is nothing more than 12 cells connected together In series. Two 12 volt batteries connected in series is nothing more than 12 cells connected together in series. So all tHings being equal there is no difference.
I suspect that what you heard started life as two GC 6v batteries are superior to one 12v battery of equivalent amp hours. This would be true because the GC 6 volt batteries are built to a much higher standard than any 12v battery. Oddly the railroad industry uses a lot of 8v batteries built to an even higher standard. So 3 railroad grade batteries will probably last longer than two 12v batteries. Not because 3 is better than 2 but because of the grade of construction.
READY
Guru
I think it would be similar IF the AH rating is the same. The major determinants for battery life are probably type of battery, depth of discharge, recharge cycle and care (if a wet battery)if you have a 12 v 200 AH AGM battery
RT Firefly
Enigma
Greetings,
Have you considered 3-8v batteries (golf cart)?
Have you considered 3-8v batteries (golf cart)?
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Mac2
Senior Member
I will be using AGM batteries due to the location of the batteries.
My post is related to a work formula (only hearsay) that states two batteries are working half as hard as one battery, thus lasting twice the lifespan as the single battery.
I'm with the other comments in that generally speaking, with flooded lead acid, golf cart batteries are a very good choice for longevity and $/AH as they are designed differently (true derp cycle) than most 12V battys meant for other applications.
GCs are available in 6V, 8V & 12V configurations. So, IMO, any combination of above in series / parallel to provide the desired V & AH should have equivalent longevity.
GCs are available in 6V, 8V & 12V configurations. So, IMO, any combination of above in series / parallel to provide the desired V & AH should have equivalent longevity.
AGM is a whole different story than FLA. Both East Penn & Trojan have confirmed that with AGM there us little or no difference in deep cycle or starting performance between GCs and other sizes (Ex: GP 31s). This is reflected in specs where with AGM they spec both AH and CCA.
The only way a pair of battys "works half as hard" as a single batty is if the AH total is 2X the single batty and it is routinely discharged half as much... but then you are comparing apples & oranges.
Cycle life is a function of DOD which is determined by AH capacity and AH used before recharge.
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Mac2
Senior Member
Thanks Bacchus! I was going to replace my 8d's with two group 31s, but it doesn't seem like any advantage, other then the ease of handling the lighter 31's.
It is still wrong in general. The 12V batteries are made up of 6 individual cells strapped together and packaged as a single case. The 24V battery is made up of 12 individual cells strapped and packaged as one. In the same brand and line the individual cells will be functionally identical. If you glue the two cases of 12V together you have a 24V. Now, there are plenty of differences between construction of various batteries which can account for large differences in longevity. These are independent of 2V, 6V, 8v, 12V, 24V, 36V etc. - that is just how many cells they packaged together.
That is exactly my plan... I'm done with 8Ds.
I think you will find GP31s are common and may be lower $ vs 8D.
You can also consider a pair of AGM GCs in series for each 8D.
Just look at AH spec & $ and decide which is better.
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Mac2
Senior Member
Looking at the numbers, AH and cost, I'm going to replace the 8D's (18 in 3 banks) with Lifeline 4D's (12 in 2 banks). I can use the same battery boxes and wiring.
I'm going with Lifeline because they are the only AGMs I've heard of that you can equalize, which will extend their life.
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Mac2
Senior Member
'Is a 24V better than a 12V?
The heat wasted is proportional to the square of the current multiplied by the resistance. Other things being equal, that would cause losses on 24v to be half those on 12v. so a 24v system is always better than a 12v system – provided you can physically fit two batteries.'
This quote is from a google search. Just found it interesting.
The heat wasted is proportional to the square of the current multiplied by the resistance. Other things being equal, that would cause losses on 24v to be half those on 12v. so a 24v system is always better than a 12v system – provided you can physically fit two batteries.'
This quote is from a google search. Just found it interesting.
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Mac2
Senior Member
The plan is to spend the majority of my time at anchor. I plan on installing solar panels to help charge the two 24v house banks. I had not considered gel batteries. I heard they were more expensive and not as hardy as AGM.
There are always exceptions to the rule. Do you have a recommendation, or experience to pass on? Always open to new ideas. I would go Lithium, but don't want to change all my systems at this time.
Thanks.
My strong recommendation is not to use 4D (and certainly not 8D) unless you are under 30 and lift a lot of weights regularly. In Lifeline, the 6V, available in three different heights and capacities (4C, 6C, L16) is where I would go. Much more manageable than 4D.
While true, a boat wired for 24V has already taken that into account, and cut the wire sizes by half, doubling the resistance. On a big complex boat, the savings in wire is where the real economy is.
READY
Guru
There is probably never a perfect time to convert to Lithium but given you plan to anchor out a lot and use solar the lighter weight, deeper discharge and fast charging would have me thinking twice about putting lead back in. But of course there are other required changes as you mention. Is that nephew on your will so you can get him back in 3-5 years? ;-)
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Mac2
Senior Member
Spot on! I am rethinking things. Simi has been giving me some good advice, and I'm starting to research that angle. "Marine how To" has a great article on LifePo4 batteries. I'm looking at the KiloVault batteries.
ranger58sb
Guru
18 8Ds? Woof!
FWIW, I've also had good success with Odyssey AGMs. Can't equalize, as far as I know, but then I got 11-12 seasons from some of their G31s... so not sure what being able to equalize might have brought to the table.
The Odyssey batteries we had tended to emphasize cranking amps over capacity (so maybe nifty for a thruster bank) with good longevity, whereas the Lifelines we had were aimed more at 1000-cycle longevity but with slightly lower cranking amps.
(I've been looking at this because I'm needing to replace three 24V banks in the not-to-distant future, two for start/house and one for thruster/inverter... so I'm intending to use Lifeline for start/house and Odyssey for thruster/inverter.)
Another FWIW, Odyssey makes a tall skinny battery that might be sorta like an 8D in capacity but you MIGHT be able to stuff four of 'em into a single 8D box. See ODS-AGM470FTT. https://www.odysseybattery.com/products/ods-agm470ftt-battery-pc1800-ft/
-Chris
READY
Guru
Mac2, another huge benefit to me with Lithium is you don't need to baby them once set up. Deep discharges can kill lead in a short time and sooner or later that happens to many of us in the real world. I love reading posts where people get 10 + years but that has just not been my experience. I have enough to worry about in life and appreciate not having batteries on that list.
To get 10+ years from AGMs, you have to treat them right and that requires a well set up charging system. Long periods on the hook are generally not the sweet spot for AGMs, because it takes a very long time (lots of solar or long genset runs) to fully charge them, and they need to be fully charged periodically to get that life. Without that charging regimen, flooded batteries can actually be better (as they tolerate operating partially charged better) and LiFePo4 are ideal.
I spend a lot of time at anchor, but rarely two days in a row so frequent long engine runs. Last year I replaced the 11 year old Lifeline bank with another, but thought hard about lithium as the price was coming down and installation experience going up. If I did it this year I'd do lithium.
I spend a lot of time at anchor, but rarely two days in a row so frequent long engine runs. Last year I replaced the 11 year old Lifeline bank with another, but thought hard about lithium as the price was coming down and installation experience going up. If I did it this year I'd do lithium.
Another consideration is weight. You're removing 1.5+ tons of ballast from your boat. The trim issue may have a negative effect, or you might appreciate it. Your assessment to make.
If you want the weight, and don't want to drastically alter your charging and support systems, then consider switching to 2v OpZS batteries. These are industrial grade and can discharge to 20%, with long 20 year lives, and watering once or twice a year at most. Available in nearly any amperage you can imagine. For the same weight you'll wind up with somewhere around 25-30kW-h of usable energy. Now you're easily running your stateroom air-conditioning at night off a nice, quiet inverter.
You may wish to consider switching to a single house bank as well. As long as you have separate starting batteries, I don't see any great advantage to having two.
If you want the weight, and don't want to drastically alter your charging and support systems, then consider switching to 2v OpZS batteries. These are industrial grade and can discharge to 20%, with long 20 year lives, and watering once or twice a year at most. Available in nearly any amperage you can imagine. For the same weight you'll wind up with somewhere around 25-30kW-h of usable energy. Now you're easily running your stateroom air-conditioning at night off a nice, quiet inverter.
You may wish to consider switching to a single house bank as well. As long as you have separate starting batteries, I don't see any great advantage to having two.
READY
Guru
Mako: I did a quick online search to look at the data sheets. Those are interesting batteries for sure. I could not see any info on charging curve, will those work with existing chargers? Also the links I hit to get pricing all took me to a "get quote" link. Is there a good online source of these batteries?
twistedtree
Guru
None of this seems to make sense. Going back to the first post, the comparison between two 12v series batteries vs a 24v battery makes no sense because nobody makes a 24V battery. So I really don’t know what we are trying to compare, or what the tech is trying to tell you.
The Ah capacity of one setup vs another will be the best indicator of expected lifespan, assuming same tech, deep cycle batteries in both cases.
So what two configurations are we comparing, ‘cause I have no idea?
The Ah capacity of one setup vs another will be the best indicator of expected lifespan, assuming same tech, deep cycle batteries in both cases.
So what two configurations are we comparing, ‘cause I have no idea?
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Mac2
Senior Member
Great advice coming in. I am completely changing my plans based on the above comments. I have three banks of 8D agm batteries. Each bank has 6 batteries. I have separate starting batteries. I am disconnecting my bilge bank, but plan to keep them in as they are low and at the center of the boat. I am now looking at LifePo4 batteries to replace the 12 8DS in the engine room-port and starboard (third of the way forward of the stern). I initially thought I had to replace a lot of my battery system. Turns out that because my house bank is completely isolated from any other systems (thrusters, and other high voltage motors) I would only need to purchase a 24volt LifePo4 charger and look at protecting the battery bank from my Inverter/charger.
My preliminary thought is to go with 4 KiloVault 300 ah LifePo4 batteries.
Question: I can put two port and starboard and have two banks, or have just one bank for ease of equal charging and balancing. Is there an advantage to either? Keep in mind I would normally have both banks running. Would it by better to have two banks and switch use back and fourth in case there was a failure, I would have a backup?
Thanks
My preliminary thought is to go with 4 KiloVault 300 ah LifePo4 batteries.
Question: I can put two port and starboard and have two banks, or have just one bank for ease of equal charging and balancing. Is there an advantage to either? Keep in mind I would normally have both banks running. Would it by better to have two banks and switch use back and fourth in case there was a failure, I would have a backup?
Thanks
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Mac2
Senior Member
I was initially thinking of using 4 group 31's (series and parallel) instead of two 8Ds for a 24volt system.
READY
Guru
2 Banks vs. 1
There are a number of items to consider I think. Without diving into this my first response would be 1 bank just to keep it simple. But some of the areas that probably come into play would be
Probably a lot of other things I am not considering including getting your solar into the batteries. Also keep in mind if you are charging these from your alternator you will need to make some modifications to avoid damaging it due to the high current consumption of the LiFePo4 batteries when charging (which is a key advantage when you want to get them topped with minimal generator or eng. run time. This should be a fun project and can be a DIY one but be sure you spend a lot of time planning and probably plan to have some help from a pro to ensure everything is done properly. This will be a big bank so sparks will fly if something is amiss
There are a number of items to consider I think. Without diving into this my first response would be 1 bank just to keep it simple. But some of the areas that probably come into play would be
- Physical location of batteries and associated chargers/inverters
- Wire runs/sizes
- Demand (if 2 banks do you have to switch it in the wee hours of the am?)
- Can you parallel 4 of these batteries (Probably yes but need to check)
Probably a lot of other things I am not considering including getting your solar into the batteries. Also keep in mind if you are charging these from your alternator you will need to make some modifications to avoid damaging it due to the high current consumption of the LiFePo4 batteries when charging (which is a key advantage when you want to get them topped with minimal generator or eng. run time. This should be a fun project and can be a DIY one but be sure you spend a lot of time planning and probably plan to have some help from a pro to ensure everything is done properly. This will be a big bank so sparks will fly if something is amiss
