Combining lead & lithium batteries

[rslifkin]

Several responders have mentioned Rod Collins (marinehowto.com) recognizing his expertise in marine battery systems. And, there are many references to AGM batteries. How many of you are aware of the fact that Rod is NOT a fan of AGM batteries? He has a long article on his website that explains why. Except for not needing to water the batteries, AGMs' offer virtually no advantage over flooded batteries, and at double (or more) the cost. I know, not common knowledge about AGMs. Meanwhile, AGMs must be recharged to 100% often lest they be damaged, whereas flooded batteries much less often. I suggest you read Rod's treatise before sending slings and arrows my way.

I agree. AGMs have some advantage, but also plenty of disadvantages (including cost). They can handle somewhat higher discharge rates (and higher bulk charge rates) than flooded (which matters in some applications, especially if there's limited room to just make the bank bigger). And they don't leak, can be mounted on their sides, etc. But if FLA will meet the need, they're certainly a lot cheaper than AGMs and a bit more abuse tolerant. And the highest quality flooded cells you can get are better (longer lasting) than the highest quality AGMs out there.

That said, a good quality AGM can live a long, healthy life if it's cared for properly.

IMO, for applications where they work well, if you need a non-flooded lead acid, gel cells can be a great choice. If cared for properly, they last a long time. But they give up a little power density, and they're no cheaper than good AGMs. And they're not tolerant of overcharging, but they're much less prone to sulfation than AGMs.

 

[Max1]

When the BMS shuts down the LFP, what powers your house loads?

When the BMS shuts down the LFP batteries, there is still plenty of voltage on the lead-acid batts.

The trick is to make sure that you have most of your power needs satisfied by the lfp's. Size your lfp's accordingly so that the lead acids take on the role if a backup power source once (if!) your lfp's are drawn down. The lead-acid batts are a min/max voltage backup. You never want to overcharge or overdraw lfp's. Similarly, if you power your lfp's from your alternator, you never want the BMS to cut off your lfp's from the alternator without some sort if protection to the alternator. Running lead/lithium in this scenario allows the Lead-acids to carry on accepting charge when the LFPs are cut off from the alternator by the BMS.

 

[catalinajack]

I agree. AGMs have some advantage, but also plenty of disadvantages (including cost). They can handle somewhat higher discharge rates (and higher bulk charge rates) than flooded (which matters in some applications, especially if there's limited room to just make the bank bigger). And they don't leak, can be mounted on their sides, etc. But if FLA will meet the need, they're certainly a lot cheaper than AGMs and a bit more abuse tolerant. And the highest quality flooded cells you can get are better (longer lasting) than the highest quality AGMs out there.

That said, a good quality AGM can live a long, healthy life if it's cared for properly.

IMO, for applications where they work well, if you need a non-flooded lead acid, gel cells can be a great choice. If cared for properly, they last a long time. But they give up a little power density, and they're no cheaper than good AGMs. And they're not tolerant of overcharging, but they're much less prone to sulfation than AGMs.

AGMs do have a higher charge rate, but, in practice, this advantage is surprisingly negligible vs flooded batteries. Take a look at Rod Collins article on charging AGMs. His extensive testing revealed that AGMs depleted to 50% SOC charge only 12 minutes faster than a like flooded battery bank.

https://marinehowto.com/how-fast-can-an-agm-battery-be-charged/

 

[catalinajack]

I tryed looking up AGM batteries on marinehowto.com on why Rod is not a fan of AGMs. I could not find it. A link would be nice.

From my experience, I had 5 AGMs from Oddessy that lasted at lest 11 years. Than I sold my boat with them. For me, peace of mind knowing that I had a batteries that just wanted to keep going was great.

I never charged them during winter months. Every spring I did a load test, all good. A little pricey, but for over 11 years of good service I am happy.

Iggy, I searched high and low on Rod Collins' website and could not locate the article that I had in mind. But, go back to Post #9, in which Rod states that he cannot understand why anyone would buy AGMs. Perhaps he will read this and provide his reasons. I may have it incorrect, but I do not think so. Given that Rod's extensive testing on charge times of AGMs vs. flooded batteries revealed that that is no significant difference, one has to wonder why anyone would choose AGMs except for convenience (watering). Even then, there are automatic watering systems available. Meanwhile, the disadvantages are significant in some use cases (inability to frequently recharge to 100% SOC).

 

[rslifkin]

AGMs do have a higher charge rate, but, in practice, this advantage is surprisingly negligible vs flooded batteries. Take a look at Rod Collins article on charging AGMs. His extensive testing revealed that AGMs depleted to 50% SOC charge only 12 minutes faster than a like flooded battery bank.

https://marinehowto.com/how-fast-can-an-agm-battery-be-charged/

That test doesn't compare AGM vs flooded at all. It only shows that cranking up the charge rate on the same bank doesn't save all that much charge time. It does nothing to test if the charge rate dropoff (and therefore time required for full charge) is different for AGM vs flooded.

That said, the ability to bulk charge AGMs quickly is mostly beneficial in limited situations. Such as having been on the hook for a couple of days when it's cloudy and solar production is low. Batteries need a boost in the morning from the generator so the solar can actually get them topped off. The batteries with the higher acceptance rate in bulk will lead to a shorter generator run to get the same amount of power added to them (and then let the solar handle the long, slow, part of the charging process).

 

[Porgy]

But, go back to Post #9, in which Rod states that he cannot understand why anyone would buy AGMs. Perhaps he will read this and provide his reasons. I may have it incorrect, but I do not think so.

Rod can certainly clarify for himself but my reading of his comment was why would anyone buy AGM compared to LFP. Not AGM vs flooded LA. I could be wrong but from my reading on his website, he is long past flooded batteries and moving into the 21st century with LFP.

 

[Iggy]

Iggy, I searched high and low on Rod Collins' website and could not locate the article that I had in mind. But, go back to Post #9, in which Rod states that he cannot understand why anyone would buy AGMs. Perhaps he will read this and provide his reasons. I may have it incorrect, but I do not think so. Given that Rod's extensive testing on charge times of AGMs vs. flooded batteries revealed that that is no significant difference, one has to wonder why anyone would choose AGMs except for convenience (watering). Even then, there are automatic watering systems available. Meanwhile, the disadvantages are significant in some use cases (inability to frequently recharge to 100% SOC).

Thank you! Its all behind me now since I did change over to lithium with my new boat last year. all I can say that my past experience with AGMs from Odyssey were good to me.

 

[Volt and Amps]

I am under the impression that the ISO regulations is specifically targeting Lithium ion batteries and not LiFePO4 batteries. Correct me if I am wrong

Reading the recent letter from the president of the ABYC where he basically is saying that they have investigated fires in boats and can not find LiFePO4 batteries being the root cause of these fires and that the organization is working on the updated recommendations it will be very interesting to see what the final take will be.

My understanding is that there would be a very big difference between hybrid banks between LiFePO4 and PbSO4 and that again the Li ion batteries have never been suggested as a good idea when creating a hybrid bank just based on the differences between the two types of Lithium chemistry?

 

[twistedtree]

I am under the impression that the ISO regulations is specifically targeting Lithium ion batteries and not LiFePO4 batteries. Correct me if I am wrong

Reading the recent letter from the president of the ABYC where he basically is saying that they have investigated fires in boats and can not find LiFePO4 batteries being the root cause of these fires and that the organization is working on the updated recommendations it will be very interesting to see what the final take will be.

My understanding is that there would be a very big difference between hybrid banks between LiFePO4 and PbSO4 and that again the Li ion batteries have never been suggested as a good idea when creating a hybrid bank just based on the differences between the two types of Lithium chemistry?

LiFePO4 batteries ARE lithium-Ion batteries, and are covered by both the ABYC and ISO specs, both of which cover all forms of Lithium-Ion batteries without further distinction. I think the risk of interconnecting lead and Lithium-Ion batteries is the same regardless of which type of lithium-ion battery is used. All can dump their full power content very quickly into a shorted lead battery, and that's the failure mode that is of concern.

 

[DDW]

Except for not needing to water the batteries, AGMs' offer virtually no advantage over flooded batteries, and at double (or more) the cost.

They do have advantages, including longer life in many situations. The advantages I pay for? No discharge of corrosive chemicals. Lower internal resistance. Longer life when well cared for (as stated, I've gotten 11 - 17 years life from them).

Rod's reservations about them have a lot to do with no one installing them correctly, with correctly set chargers and charging practice. Flooded batteries are more tolerant of mistreatment. If you buy batteries to mistreat, buy flooded - they will deal with it better and are cheaper to replace when you murder them.

I don't think any LA batteries have much product life left in them. 10 years from now you may even have trouble finding them. Lithium are taking over at an accelerated pace.

 

[Bacchus]

They [Edit AGMs] do have advantages, including longer life in many situations. The advantages I pay for? No discharge of corrosive chemicals. Lower internal resistance. Longer life when well cared for (as stated, I've gotten 11 - 17 years life from them).



Rod's reservations about them have a lot to do with no one installing them correctly, with correctly set chargers and charging practice. Flooded batteries are more tolerant of mistreatment. If you buy batteries to mistreat, buy flooded - they will deal with it better and are cheaper to replace when you murder them.



I don't think any LA batteries have much product life left in them. 10 years from now you may even have trouble finding them. Lithium are taking over at an accelerated pace.

I'm in the camp that still have and believe in AGM.
I fully respect Rods / CMS points that may apply to many others.
My rationale... that may apply to a small sub-set or maybe none but here is why I do what I do.

I'm done with FLA corrosion, refurbing motorhome batty bays / slides, etc
I dont plan on motorhoming or boating forever... and may be out of one or both within 5 yrs +/-
I dont have a relative that will inherit / benefit from the long term (I only buy ripe / not green bananas)
I dont look at battys as an "investment" with a 10-20 yr breakeven/ payback
My current boat AGMs (start and house) are 8+ yrs old and still doing OK
I plan to replace them with AGM when/if needed but will NOT buy another 8D AGM as I can replace them w/ (2) GP31 AGMs for less $
I have start / thruster banks separate from house and ACR / ALT and multi bank shore charger that serves both effectively for my use
I'm not interested in mixing chemistry and needing to add DC to DC charging at an additional $
No solar in my case
My MH start bank of 2 GP 31 maint free were 10 yrs old when I replaced them not because they failed but were testing around 50% of rated CCA... I'll take that any day for good performance.
I have other minor advantages I believe in for AGMs but others may be in very different environment & usage / storage conditions

I get that others have their reasons and justifications that may not line up... and thats OK
I still say LiFePO are not for everyone in every case... Yet.... maybe in the future when OEM systems are already in place and their replacement is obvious and they work fir ALL without system modifications.

 

[Max1]

LiFePO4 batteries ARE lithium-Ion batteries, and are covered by both the ABYC and ISO specs, both of which cover all forms of Lithium-Ion batteries without further distinction. I think the risk of interconnecting lead and Lithium-Ion batteries is the same regardless of which type of lithium-ion battery is used. All can dump their full power content very quickly into a shorted lead battery, and that's the failure mode that is of concern.

Aw HELL **NO**!!!!
LiFe, LiOn, LiPo are all *completely* different batteries in terms of chemistry, voltage, carge types and RISKS!!!

*They cannot be handled in the same manner.*

Although benign in the hands of knowledgeable users, lipo is most dangerous with the highest chance of starting a fire in the hands of incompetent users. LiPo voltage range is not compatible with 12V systems. For marine use, avoid using LiPo at all costs.

LiOn is safer than LiPo, but voltage is not compatible with 12v systems. You can probably use LiOn and LiPo on 24 volt systems or higher, but why would you do that when you can use LiFe?

LiFe batteries are the safest of all three chemistries. They are less likely to catch fire, and more tolerant to abuse than the other two lithium chemistries. LiFe voltage is also compatible with 12 volt and 24 volt systems. Given that they are much safer, why use LiPo or LiOn?

In summary, the above three battery types are not the same. Anyone who tells you they are doesn't know what they're talking about.

Edit- sorry for the rant above, but I take battery safety very seriously. Anyone who misunderstands how the three lithium battery types operate is likely to make a huge mistake which would probably result in a fire. As I say to everyone who asks me about lithium batteries. If you don't know how to handle them don't take a chance and do something stupid. In that case, Stick with conventional battery types.

 

[Delfin]

Aw HELL **NO**!!!!
LiFe, LiOn, LiPo are all *completely* different batteries in terms of chemistry, voltage, carge types and RISKS!!!

*They cannot be handled in the same manner.*

Although benign in the hands of knowledgeable users, lipo is most dangerous with the highest chance of starting a fire in the hands of incompetent users. LiPo voltage range is not compatible with 12V systems. For marine use, avoid using LiPo at all costs.

LiOn is safer than LiPo, but voltage is not compatible with 12v systems. You can probably use LiOn and LiPo on 24 volt systems or higher, but why would you do that when you can use LiFe?

LiFe batteries are the safest of all three chemistries. They are less likely to catch fire, and more tolerant to abuse than the other two lithium chemistries. LiFe voltage is also compatible with 12 volt and 24 volt systems. Given that they are much safer, why use LiPo or LiOn?

In summary, the above three battery types are not the same. Anyone who tells you they are doesn't know what they're talking about.

Edit- sorry for the rant above, but I take battery safety very seriously. Anyone who misunderstands how the three lithium battery types operate is likely to make a huge mistake which would probably result in a fire. As I say to everyone who asks me about lithium batteries. If you don't know how to handle them don't take a chance and do something stupid. In that case, Stick with conventional battery types.

I believe you just told Einstein he doesn't know anything about math. Nice.

 

[twistedtree]

Aw HELL **NO**!!!!
LiFe, LiOn, LiPo are all *completely* different batteries in terms of chemistry, voltage, carge types and RISKS!!!

I agree there are lots of differences between the different chemistries, but I frankly don't understand what chemistries you are referring to here since none of your nomenclature is commonly used.


By LiFe, I suspect you mean LiFePO4 or LFP?

I don't know what what chemistry you mean by LiOn?


By LiPo I think you are referring to Lithium Polymer which is really just a construction method for one of the common types like LCO or LMO using a polymer electrolyte rather than a liquid.



Here are some of the more common Lithium-ion chemistries, and I will reiterate that they are ALL forms of lithium-ion batteries.



Here is a good reference: https://batteryuniversity.com/article/bu-205-types-of-lithium-ion
Lithium Cobalt Oxide(LiCoO2) — LCO

Lithium Manganese Oxide (LiMn2O4) — LMO

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC

Lithium Iron Phosphate(LiFePO4) — LFP


Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA

Lithium Titanate (Li2TiO3) — LTO

 

[Airstream345]

Max1 - Confused by your reply to twistedtree - LiFePO4 = Lithium Iron Phosphate. According to everyone and Wikipedia: "The lithium iron phosphate battery is a type of lithium-ion battery using lithium iron"

Appreciate you calling out the differences however we're talking LiFePO4 here.

 

[SteveK]

Confused more. I am coming around to considering LI.
Now more variables, which Lithium to get.

 

[Insequent]

Confused more. I am coming around to considering LI.
Now more variables, which Lithium to get.

No need to be confused. In practice there is only one choice for boats at this point: LFP

Go to the link TT posted and look at the "Thermal Runaway" comment in the summary for each battery type, as well as cost/kWh (where quoted).

 

[twistedtree]

No need to be confused. In practice there is only one choice for boats at this point: LFP

Exactly. It's the only sensible choice for a boat, and what is predominantly available for house batteries. Where the other more volatile variants will appear is in water toys, scooters, and propulsion motors. All these should be treated with a heightened level of care, charged on a non-flammable surface, and not left on a charger when the boat isn't attended.

 

[catalinajack]

That test doesn't compare AGM vs flooded at all. It only shows that cranking up the charge rate on the same bank doesn't save all that much charge time. It does nothing to test if the charge rate dropoff (and therefore time required for full charge) is different for AGM vs flooded.

That said, the ability to bulk charge AGMs quickly is mostly beneficial in limited situations. Such as having been on the hook for a couple of days when it's cloudy and solar production is low. Batteries need a boost in the morning from the generator so the solar can actually get them topped off. The batteries with the higher acceptance rate in bulk will lead to a shorter generator run to get the same amount of power added to them (and then let the solar handle the long, slow, part of the charging process).

Does it not say that the AGMs charged 12 minutes faster? Faster than what? When that test was done, the only other technology that existed was flooded. I guess I missed something.

 

[rslifkin]

Does it not say that the AGMs charged 12 minutes faster? Faster than what? When that test was done, the only other technology that existed was flooded. I guess I missed something.

The test was just charging the same AGM battery at 2 different rates (0.2C in bulk and 0.4C in bulk). There was no flooded battery involved in the test. So it's a test of how much you'd gain from a bigger charger, not AGM vs flooded.

 

[catalinajack]

Aw HELL **NO**!!!!
LiFe, LiOn, LiPo are all *completely* different batteries in terms of chemistry, voltage, carge types and RISKS!!!

*They cannot be handled in the same manner.*

Although benign in the hands of knowledgeable users, lipo is most dangerous with the highest chance of starting a fire in the hands of incompetent users. LiPo voltage range is not compatible with 12V systems. For marine use, avoid using LiPo at all costs.

LiOn is safer than LiPo, but voltage is not compatible with 12v systems. You can probably use LiOn and LiPo on 24 volt systems or higher, but why would you do that when you can use LiFe?

LiFe batteries are the safest of all three chemistries. They are less likely to catch fire, and more tolerant to abuse than the other two lithium chemistries. LiFe voltage is also compatible with 12 volt and 24 volt systems. Given that they are much safer, why use LiPo or LiOn?

In summary, the above three battery types are not the same. Anyone who tells you they are doesn't know what they're talking about.

Edit- sorry for the rant above, but I take battery safety very seriously. Anyone who misunderstands how the three lithium battery types operate is likely to make a huge mistake which would probably result in a fire. As I say to everyone who asks me about lithium batteries. If you don't know how to handle them don't take a chance and do something stupid. In that case, Stick with conventional battery types.

I don't think twistedtree misunderstands the different chemistry one bit. He was merely pointing out that the ISO/ABYC advice applies equally and to all chemistries.

 

[catalinajack]

Well, guys, I have no problem using flooded batteries. They work for me. They are way cheaper. I have eight golf car batteries that are now five years old and test to 97% of original capacity. I suspect that in 4 or 5 years, I will need to replace them at (today's) cost of about $1,300 for a set of Trojans. For my use case, they do just fine. Call me a luddite if you will, but lithium is NOT the answer for all use cases and all budgets.

Look, it is obvious, from this discussion and many discussions on this forum, that moving to lithium requires a complete newly-engineered system at a very high cost. For many of us, that cost is simply not worth the price of admission. It seems that some here are so enamored of lithium that you refuse to recognize that sticking with flooded can be a good choice for many. And by the way, my battery box has ZERO corrosion.

 

[catalinajack]

The test was just charging the same AGM battery at 2 different rates (0.2C in bulk and 0.4C in bulk). There was no flooded battery involved in the test. So it's a test of how much you'd gain from a bigger charger, not AGM vs flooded.

Yes, correct, but look at how fast the AGMs move from bulk to absorb. And, how many boats have chargings systems capable of delivering a charge of 0.2C? Not many. As I recall, Rod takes note of that in his write-up. Without that ability, AGMs lose that quick-charge ability quickly.

All I know is that it takes 5.5 hours to charge my 920Ah flooded bank to 100% from 50% SOC. How much faster would an AGM bank of an equally size take, I do not know, but I suspect not much faster. Plus, flooded batteries do not need to be taken all the way to 100% frequently as do AGMs.

 

[rslifkin]

Well, guys, I have no problem using flooded batteries. They work for me. They are way cheaper. I have eight golf car batteries that are now five years old and test to 97% of original capacity. I suspect that in 4 or 5 years, I will need to replace them at (today's) cost of about $1,300 for a set of Trojans. For my use case, they do just fine. Call me a luddite if you will, but lithium is NOT the answer for all use cases and all budgets.

Look, it is obvious, from this discussion and many discussions on this forum, that moving to lithium requires a complete newly-engineered system at a very high cost. For many of us, that cost is simply not worth the price of admission. It seems that some here are so enamored of lithium that you refuse to recognize that sticking with flooded can be a good choice for many. And by the way, my battery box has ZERO corrosion.

I'm still using AGMs on my boat. At this point, LFP would be a bit more expensive (but not dramatically from what I've seen) and I'd have to re-design the alternator to house battery charging setup (the rest of my equipment would just need settings adjusted). So up to this point, being that the AGMs work fine for my use case, I haven't felt a reason to switch. I figure I'll assess again when I'm due to replace batteries or have a reason to make other changes and then see how it all looks at that point.

Yes, correct, but look at how fast the AGMs move from bulk to absorb. And, how many boats have chargings systems capable of delivering a charge of 0.2C? Not many. As I recall, Rod takes note of that in his write-up. Without that ability, AGMs lose that quick-charge ability quickly.

All I know is that it takes 5.5 hours to charge my 920Ah flooded bank to 100% from 50% SOC. How much faster would an AGM bank of an equally size take, I do not know, but I suspect not much faster. Plus, flooded batteries do not need to be taken all the way to 100% frequently as do AGMs.

Charging-wise, the best I can do from the engine alternators or solar is about 0.14C on my boat. The inverter/charger is big enough to provide just under 0.2C, however. Interestingly, I've found that while my AGMs will accept more than 0.2C until they're up to somewhere around 80%, if you try to feed them 0.2C or higher continuously they start to get rather warm (but 0.15C causes only a slight temperature increase). One day when they were a bit low, but charging from solar, I fired up the generator for something and found that I was pushing power into the batteries at about 0.25C. At that rate, the battery temps started climbing pretty rapidly and actually got hot enough that the solar dropped to float and the inverter stopped charging until the batteries cooled a bit (around 120* F).

Getting from 50% to truly 100% topped off in 5.5 hours with any lead chemistry is pretty unlikely. 99% is quite possible, but truly topped off takes a lot longer. With a 920ah bank, you'd have 460ah to make up. Assuming you're charging at 100 amps and you make it to 90% before getting to absorption voltage and the resulting current tapering, you'd be in bulk for about 3:45 to get to 90% SoC. I'd expect 1.5 - 3 hours in absorption depending on the batteries and your end absorb target. But even then, they'll still be taking some power once the charger drops to float, so they're not quite full (although close enough on flooded batteries that get equalized periodically, especially if they do see a longer float sometimes).

As an example, for my Fullriver AGMs, the recommended charging profile is to bulk to 14.7 volts, absorb at 14.7 volts until current is down to 0.02 - 0.012C, then float at 13.65 volts for 8 hours before they're considered truly full. Realistically, that'll only ever happen when we're on shore power, so I have my solar keep them in absorb down to 0.01C, figuring the slightly longer absorption phase will get them closer to topped off when they only get a couple/few hours of float before the sun goes down.

 

[Volt and Amps]

Dear twistetree, thank you for your input and interesting views!

Lithium for sure has a lot of interesting very different chemistries and it can sometimes be a bit confusing since they are being named differently when abbreviations are used.
For sure LiFePO4 is the only interesting version and the one we are talking about here.
Just to go back to the ISO and ABYC recommendations and what is in their "regulations".
You stated in an earlier post that the ban on using different chemistries in the same bank should be interpreted as a ban on combining LiFePO4 and PBSO4 in a commonly connected bank. I am not so sure that this is the correct interpretation or the purpose behind the recommendation.
I guess ( for sure I will get in contact with them and get it verified or falsified) that the very logical and sensible interpretation is that these organizations are telling the industry not to ever mix different Lithium chemistry in the same bank. The paragraph is under a subchapter relating to what you correctly pointed out is all Lithium chemistry.

My understanding right or wrong is that the recommendation is referring to Lithium battery technology and only that. I am sticking out my neck a bit further saying that there is no recommendations regarding what this thread essentially is about, a hybrid LiFePO4 and PbSO4 hybrid battery.
If such a recommendation would exist I actually guess it would have its own very specific chapter with all details.
I also guess this idea is far too new and with very few actors in a very early stage of trying the idea in real-life applications, there simply is too little knowledge and facts for the ISO or ABYC to base any new recommendations on.

I was actually spending some time thinking about what you wrote regarding the risk of an internal short in a lead acid cell and a dangerous situation created by the Lithium part of the bank "pumping" energy into the failing cell.
It is interesting, my initial thinking about this scenario is that we might actually sit on thousands of experiments a day in the world where just this scenario actually is tested. Using jump cables starting a car with a bad or low SOC Pb from a donor car with its engine running.
Think about it, if we look at the situation when the donor car is providing a voltage actually higher initially than when a LiFePO4 bank would supply a failed Pb cell it is in many ways a more dramatic high amp occurrence when connecting the jumper cables compared to even a hybrid bank constantly connected without a smart device that disconnects the Li either by itself or via the BMS overcurrent protection.

I am looking forward to your input that most likely will give me more food for thoughts about this situation.
For sure I am personally very interested in the possibilities of the hybrid bank approach
and I am actively thinking about redoing my yacht in this way I believe is not only extremely cost-effective but also actually increasing safety compared to an all-lithium approach.
Thinking about it I actually think a Lead portion ought to be mandatory for vessels with only electrical propulsion in order to have some emergency backup to what most likely will be a big lithium based energy bank.

 

[SteveK]

No need to be confused. In practice there is only one choice for boats at this point: LFP

Go to the link TT posted and look at the "Thermal Runaway" comment in the summary for each battery type, as well as cost/kWh (where quoted).

LFP. Is the LiFePO4 one of or the ONLY LFP

 

[DDW]

The Lifeline AGMs in my sailboat would accept over 0.5C when discharged to 50% SOC. This would drop to about 0.2C by 80% SOC. They would not temperature limit. That is faster than flooded cells are likely to charge. However the weak point of AGMs is the need to fully recharge periodically (like weekly at least), and that takes just as long with flooded as AGM. It is best for flooded to also recharge fully, but they can be equalized to minimize the sulfation that results from partial state of charge.

LFP are really much better suited to the task of live aboard boating. Their downside is the complexity of installation and management. Lifecycle costs now favor them.

 

[Insequent]

LFP. Is the LiFePO4 one of or the ONLY LFP

LFP is the common abbreviation of LiFePO4

 

[SteveK]

LFP is the common abbreviation of LiFePO4

Thank you. For a moment I thought that would narrow down the search, , nope, they come in 50, 100, 200 and maybe more Ah. Various colors and brands. Some look like 8D flooded. Then the cost differential.

So if I want to get 400 Ah, is it better with 4-100 or 2-200? if it matters for usage that is.

 

[twistedtree]

Dear twistetree, thank you for your input and interesting views!

Lithium for sure has a lot of interesting very different chemistries and it can sometimes be a bit confusing since they are being named differently when abbreviations are used.
For sure LiFePO4 is the only interesting version and the one we are talking about here.
Just to go back to the ISO and ABYC recommendations and what is in their "regulations".
You stated in an earlier post that the ban on using different chemistries in the same bank should be interpreted as a ban on combining LiFePO4 and PBSO4 in a commonly connected bank. I am not so sure that this is the correct interpretation or the purpose behind the recommendation.
I guess ( for sure I will get in contact with them and get it verified or falsified) that the very logical and sensible interpretation is that these organizations are telling the industry not to ever mix different Lithium chemistry in the same bank. The paragraph is under a subchapter relating to what you correctly pointed out is all Lithium chemistry.

My understanding right or wrong is that the recommendation is referring to Lithium battery technology and only that. I am sticking out my neck a bit further saying that there is no recommendations regarding what this thread essentially is about, a hybrid LiFePO4 and PbSO4 hybrid battery.
If such a recommendation would exist I actually guess it would have its own very specific chapter with all details.
I also guess this idea is far too new and with very few actors in a very early stage of trying the idea in real-life applications, there simply is too little knowledge and facts for the ISO or ABYC to base any new recommendations on.

I was actually spending some time thinking about what you wrote regarding the risk of an internal short in a lead acid cell and a dangerous situation created by the Lithium part of the bank "pumping" energy into the failing cell.
It is interesting, my initial thinking about this scenario is that we might actually sit on thousands of experiments a day in the world where just this scenario actually is tested. Using jump cables starting a car with a bad or low SOC Pb from a donor car with its engine running.
Think about it, if we look at the situation when the donor car is providing a voltage actually higher initially than when a LiFePO4 bank would supply a failed Pb cell it is in many ways a more dramatic high amp occurrence when connecting the jumper cables compared to even a hybrid bank constantly connected without a smart device that disconnects the Li either by itself or via the BMS overcurrent protection.

I am looking forward to your input that most likely will give me more food for thoughts about this situation.
For sure I am personally very interested in the possibilities of the hybrid bank approach
and I am actively thinking about redoing my yacht in this way I believe is not only extremely cost-effective but also actually increasing safety compared to an all-lithium approach.
Thinking about it I actually think a Lead portion ought to be mandatory for vessels with only electrical propulsion in order to have some emergency backup to what most likely will be a big lithium based energy bank.

I can dig out the language later for both ABYC and ISO, but I believe the intent is to address exactly this situation. Batteries in a bank should all be the same chemistry, period. But by all means send in a Request For Interpretation. We will take it up at the next meeting.

I get the attraction to a hybrid bank, but really think that in the end is totally motivated by drop in batteries that don’t provide basic control signals as better BMSes do. With the most basic signals; Allow to Charge, and Allow to Discharge, alternators can be easily and gracefully turned off, and any need for a hybrid bank goes away. The hybrid is just a way to hack around incomplete BMSes.