Lithium Batteries

[Tally Ho]

I got out to check the batteries today, and I captured the charger info as well…and I feel better today seeing the battery voltages and SOC’ s.

first, charger reports…I turned off power to go to the fuel dock and pump out, and then turned the power off again to check something else…so ypu see a few short charges most recently. But you see a few longer duration charge cycles as well.


here are the charger settings for Li-ion…


and here are the battery statuses: Both batteries had exact same voltage, but SOC was off by 1%.
neither battery “disconnected” the Charge MOSFET.


I can probably live with this for my limited power needs.

Greg

 

[dlochner]

and here are the battery statuses: Both batteries had exact same voltage, but SOC was off by 1%.
neither battery “disconnected” the Charge MOSFET.

That 1% difference may be due to cell balancing. The second battery was still balancing the cells.

 

[Johann]

Both batteries had exact same voltage, but SOC was off by 1%.
neither battery “disconnected” the Charge MOSFET.

Nice. It’s possible one battery had a greater cell imbalance initially and needed a couple of charge cycles to get the cells closer. Maybe that was the cause of a higher level of protection preventing it from discharging before.

 

[High Current]

So far, there is no evidence that LFP batteries can go into a thermal runaway and cause a fire.

As respectfully but emphatically as possible, THIS IS WRONG!!! It is a common and understandable misconception, but also a dangerous one! In the article referenced below, the researchers used an adiabatic chamber (neither adds nor removes heat from the system) and slowly raised the temperature of the battery until it started heating itself - no over-charging or other abuse required.

https://jeas.springeropen.com/articles/10.1186/s44147-025-00668-y

LFP does experience thermal runaway. The temperature of onset is higher (i.e. it is more resistant to it) and the peak temperatures are lower, so it is definitely safeER than other chemistries, but not "safe." It can still produce flammable gas, and if the failure or heat causes an internal short, it may also produce an ignition source. Under the right conditions, an LFP battery can definitely ignite, and the result is not trivial:

Point being: treat LFP with the same respect you would any lithium battery. Buy reputable batteries and chargers. Follow ABYC guidelines. Don't go hooking them directly up to your alternator / starter (unless they are rated for such). And then enjoy the peace of mind knowing your house bank is comparatively safer than your laptop/phone/tablet/speaker/EV/shaver/e-bike/etc.

 

[dlochner]

As respectfully but emphatically as possible, THIS IS WRONG!!! It is a common and understandable misconception, but also a dangerous one! In the article referenced below, the researchers used an adiabatic chamber (neither adds nor removes heat from the system) and slowly raised the temperature of the battery until it started heating itself - no over-charging or other abuse required.

https://jeas.springeropen.com/articles/10.1186/s44147-025-00668-y

LFP does experience thermal runaway. The temperature of onset is higher (i.e. it is more resistant to it) and the peak temperatures are lower, so it is definitely safeER than other chemistries, but not "safe." It can still produce flammable gas, and if the failure or heat causes an internal short, it may also produce an ignition source. Under the right conditions, an LFP battery can definitely ignite, and the result is not trivial:

Point being: treat LFP with the same respect you would any lithium battery. Buy reputable batteries and chargers. Follow ABYC guidelines. Don't go hooking them directly up to your alternator / starter (unless they are rated for such). And then enjoy the peace of mind knowing your house bank is comparatively safer than your laptop/phone/tablet/speaker/EV/shaver/e-bike/etc.

I've seen that video and that is not thermal runaway. It is the electrolyte in the cell burning after the cell had been abused and punctured. What that video shows is an ordinary fire, i.e., the rapid oxidation of the electrolyte. Cut off the oxygen supply and the fire goes out.

Thermal runaway is not a typical fire and it can not be put out by typical fire fighting methods, such as CO2 extinguishers, water or foam. It will continue because it is a reaction between the chemicals inside the battery. A thermal runaway could occur even if the battery was in a vacuum with no oxygen. The only way to stop a thermal runaway is to remove the heat generated by the reaction faster than the reaction is generating the heat. No fire extinguisher or water hose can do that.

A LFP battery is an energy source and like any energy source, a gallon of gas, a bottle of propane, a LA battery, it has to be treated with some care and not abused or subjected to misuse. The danger of LFP going in to a thermal runaway situation is just about nil. The battery's chemistry just doesn't allow it and no one has been able to induce a thermal runaway in an LFP battery. There a many people who would love to see evidence of a thermal runaway in a LFP battery, however, in some 20 years of use, there are no documented cases of LFP batteries going into thermal runaway. That is not the case with other Lithium Ion batteries. Remember those Samsung phones that went up in flames?

 

[High Current]

I've seen that video and that is not thermal runaway. It is the electrolyte in the cell burning after the cell had been abused and punctured. What that video shows is an ordinary fire, i.e., the rapid oxidation of the electrolyte. Cut off the oxygen supply and the fire goes out.

It sounds like we are using the same term to describe different things.

It sounds like you are using the term "thermal runaway" to describe the chemical fire that occurs after the cell has already failed, specifically one in which the battery contains its own oxidizer and can therefore burn without an air supply. We are agreed that LFP doesn't explode as dramatically as cobalt cells - or most other fuels for that matter. In many cases it doesn't even self-ignite, but I'm not going to bet my boat on it.

From an engineering perspective, "Thermal Runaway" is a phenomenon whereby a device, once it reaches a critical temperature, begins to heat itself, and the hotter it gets the faster it heats itself, until it fails. In batteries, it occurs because heat accelerates self-discharge, and above a critical threshold it generates more heat internally than it can dissipate through the case. Even lead acid can exhibit this effect under the right conditions, but with a water-based electrolyte, the results are seldom if ever dramatic. For lithium cobalt, the paper I linked shows this runaway can start around 100C, while for LFP it's a higher 124C.

Staying away from the thermal runaway threshold is why over-temperature protection is one of the essential features of a good BMS. The reason quality is important is because poor cell quality or a shoddy BMS can create internal sources of over-temperature that the BMS cannot stop.

 

[marcham]

Thermal runway, or combustible gases, the common point in the posts above is that like many other products on a boat, there is an increased potential for fire as a result of installing a lithium house/starter bank, compared to not having them onboard. A malfunctioning cell phone can be tossed in a sink and water poured over top, the same can't be done with a ship's house battery bank. To say they are 100% safe and can be dropped in like any other chemistry battery without understanding the exact battery installed, vessel and systems they are going into would be foolish. Like anything else that burns, can ignite or produce a lot of heat on a boat (flares, fuel, propane, wood, high current electrical), it just has to be managed and installed with care and attention.

To say that LFP(lifepo4) has no fire risks because they can't go into thermal runaway (which is very often posted here, on other forums and with some "experts" on youtube), is probably not be best advice for someone that's just getting into lithium. The truth is that they are much less likely than other lithium chemistries to go into thermal runway. They can vent hydrogen and that is very combustible. A lead acid battery also produces Hydrogen gas ... thus why they have to be installed in a certain way to avoid explosions.

Pouch, prismatic and cylindrical Lifepo4 cells each have different mechanical properties. They can have thermal runaways through various mechanism when physically abused, incorrectly installed or charged outside of their manufacturer recommended parameters.

• Sun, T. et al. "Thermal Runaway Characteristics and Modeling of LiFePO₄ Power Battery for Electric Vehicles" (2023) SpringerLink
  • This article presents adiabatic tests on LFP batteries at various states of charge (SOC) and shows that TR (thermal runaway) severity increases with SOC. They identify characteristic temperatures for onset, etc., extract kinetics parameters of exothermic reactions, and build TR models. SpringerLink
  • Being adiabatic tests means heat removal is limited, so self-heating can escalate. It demonstrates that under those conditions, LFP cells can and do runaway.
• Chai, Zhixiong; Li, Junqiu; et al. "Experimental analysis and safety assessment of thermal runaway behavior in lithium iron phosphate batteries under mechanical abuse" (Scientific Reports, 2024) PMC
  • They used mechanical abuse (crushing, puncture, etc.) on LFP cells with different SOCs, measured temperature, voltage, force during failure, and observed thermal runaway. PMC
  • They also established regression models for safety boundaries and thermal runaway risk under mechanical abuse.
• Peng, G. et al. "Thermal Runaway Features of Large-Format Power Lithium-Ion (68Ah) LFP Cells" (2023) PMC
  • This work shows that a fully charged 68 Ah LFP cell can release on the order of 6.7 MJ of heat during thermal runaway. That level of heat release implies substantial risk and proves that LFP cells do have thermal runaway potential. PMC
• Investigating the Thermal Runaway Characteristics of Prismatic LFP Cells under Overcharge Conditions (J. Tian et al., 2025) MDPI
  • They systematically examined overcharge-induced thermal runaway in prismatic LFP cells under different ambient temperatures and charge rates. They find that both higher charge rates and higher ambient temperatures can precipitate thermal runaway. MDPI

To say that there is 0 chance of thermal runway for LFP cells is propagating misinformation; scientific research and manufacturer's own published data does not support that conclusion. Yes, they are much much less likely to do so. Properly installed, built and with a good BMS, they are likely just as safe, if not safer than flooded/AGM batteries (my opinion) due to the multi-layered protection. Some new LFP packs even have a built-in fire extinguishers. Would manufacturers do that just for the added expense?? Unlikely.

If one looks up the cell manufacturer datasheet for a CATL 314 Ah or basically any other Lifepo4 cell, there are multiple conditions listed that will result in fire. Thermal runaway, fire, explosion, producing combustible gases, really, what does it matter? They likely have the same result onboard a boat.

The key point is a prudent boater would buy quality battery, as there is extensive evidence that "cheap" batteries can have poor construction/assembly, mismatched cells that increase likelihood of cell overvoltage and BMS that don't actually have safety features that they advertise. Unlike an electric scooter, car, etc..., we can't just step off onto the sidewalk when 300 NM from shore!

Has the OP selected a battery yet? I think that was the original question...

 

[dlochner]

It sounds like we are using the same term to describe different things.

Yes.

It sounds like you are using the term "thermal runaway" to describe the chemical fire that occurs after the cell has already failed, specifically one in which the battery contains its own oxidizer and can therefore burn without an air supply. We are agreed that LFP doesn't explode as dramatically as cobalt cells - or most other fuels for that matter. In many cases it doesn't even self-ignite, but I'm not going to bet my boat on it.

Not quite. See Post #46. A thermal runaway is not a fire. It does not need an oxidizer. It is not necessarily an explosion. It is simply the result of two chemicals in an exothermic reaction that has gotten out of control, the heat generated from the reaction accelerates the reaction which provides more heat which further accelerates the reaction. Nothing is on fire, although flammable substances adjacent to the runaway reaction, including electrolytes, can and do catch fire due to the heat generated by the thermal runaway. In the case of physical abuse, as shown in a video posted earlier, it was the physical abuse that ignited the electrolyte.

From an engineering perspective, "Thermal Runaway" is a phenomenon whereby a device, once it reaches a critical temperature, begins to heat itself, and the hotter it gets the faster it heats itself, until it fails.

Yes, it becomes self-sustaining until all the reacting chemicals have reached a more stable form.

In batteries, it occurs because heat accelerates self-discharge, and above a critical threshold it generates more heat internally than it can dissipate through the case.

According to the most recent research (thank you @marcham), thermal runaway in LFP batteries occurs as a function of ambient temperature and charge rate which are synergistic. Charge rates above 1C are more likely to initiate a thermal runaway.

For lithium cobalt, the paper I linked shows this runaway can start around 100C, while for LFP it's a higher 124C.

124° C (255°F) is quite warm, perhaps more importantly the max temp for LFP is about half that of lithium Cobalt, at 421°C vs 749°C


Sailors have a long history of using precise language aboard ships, we don't have ropes and strings, the have halyards, sheets, rodes, and so on. The purpose of that precise language is clarity of communication. There is a lesson in that language use for us when talking about other things in which precise language will reduce confusion and increase clarity. Discussions about LiFePO4 batteries is an area that is desperately in need of greater clarity and dissemination of reliable scientific research.

The article I cited above is the first good evidence that I have read demonstrating LFP batteries can go into thermal runaway and showing the consequences of the reaction, venting and igniting the electrolyte. Just as important, it describes the specific conditions under which it can occur, high charge currents and high ambient temperatures. As we look to our own LFP installations, we can guard against these conditions by limiting charge currents and improving ventilation and cooling in the battery compartment.

Jamming a spike in to a LFP cell to ignite the electrolyte might make dramatic video, but it does little to educate about the inherent risks and risk mitigation we need to install a safe LFP system. The take away? Don't abuse the battery.

• Keep LFP batteries cool with good ventilation
• Keep the charging rate below 1C and follow the manufacturer's recommendation for max charge rate and voltages.

Simple enough.

 

[dlochner]

Thermal runway, or combustible gases, the common point in the posts above is that like many other products on a boat, there is an increased potential for fire as a result of installing a lithium house/starter bank, compared to not having them onboard. A malfunctioning cell phone can be tossed in a sink and water poured over top, the same can't be done with a ship's house battery bank. To say they are 100% safe and can be dropped in like any other chemistry battery without understanding the exact battery installed, vessel and systems they are going into would be foolish. Like anything else that burns, can ignite or produce a lot of heat on a boat (flares, fuel, propane, wood, high current electrical), it just has to be managed and installed with care and attention.

To say that LFP(lifepo4) has no fire risks because they can't go into thermal runaway (which is very often posted here, on other forums and with some "experts" on youtube), is probably not be best advice for someone that's just getting into lithium. The truth is that they are much less likely than other lithium chemistries to go into thermal runway. They can vent hydrogen and that is very combustible. A lead acid battery also produces Hydrogen gas ... thus why they have to be installed in a certain way to avoid explosions.

Pouch, prismatic and cylindrical Lifepo4 cells each have different mechanical properties. They can have thermal runaways through various mechanism when physically abused, incorrectly installed or charged outside of their manufacturer recommended parameters.

• Sun, T. et al. "Thermal Runaway Characteristics and Modeling of LiFePO₄ Power Battery for Electric Vehicles" (2023) SpringerLink
  • This article presents adiabatic tests on LFP batteries at various states of charge (SOC) and shows that TR (thermal runaway) severity increases with SOC. They identify characteristic temperatures for onset, etc., extract kinetics parameters of exothermic reactions, and build TR models. SpringerLink
  • Being adiabatic tests means heat removal is limited, so self-heating can escalate. It demonstrates that under those conditions, LFP cells can and do runaway.
• Chai, Zhixiong; Li, Junqiu; et al. "Experimental analysis and safety assessment of thermal runaway behavior in lithium iron phosphate batteries under mechanical abuse" (Scientific Reports, 2024) PMC
  • They used mechanical abuse (crushing, puncture, etc.) on LFP cells with different SOCs, measured temperature, voltage, force during failure, and observed thermal runaway. PMC
  • They also established regression models for safety boundaries and thermal runaway risk under mechanical abuse.
• Peng, G. et al. "Thermal Runaway Features of Large-Format Power Lithium-Ion (68Ah) LFP Cells" (2023) PMC
  • This work shows that a fully charged 68 Ah LFP cell can release on the order of 6.7 MJ of heat during thermal runaway. That level of heat release implies substantial risk and proves that LFP cells do have thermal runaway potential. PMC
• Investigating the Thermal Runaway Characteristics of Prismatic LFP Cells under Overcharge Conditions (J. Tian et al., 2025) MDPI
  • They systematically examined overcharge-induced thermal runaway in prismatic LFP cells under different ambient temperatures and charge rates. They find that both higher charge rates and higher ambient temperatures can precipitate thermal runaway. MDPI

To say that there is 0 chance of thermal runway for LFP cells is propagating misinformation; scientific research and manufacturer's own published data does not support that conclusion. Yes, they are much much less likely to do so. Properly installed, built and with a good BMS, they are likely just as safe, if not safer than flooded/AGM batteries (my opinion) due to the multi-layered protection. Some new LFP packs even have a built-in fire extinguishers. Would manufacturers do that just for the added expense?? Unlikely.

If one looks up the cell manufacturer datasheet for a CATL 314 Ah or basically any other Lifepo4 cell, there are multiple conditions listed that will result in fire. Thermal runaway, fire, explosion, producing combustible gases, really, what does it matter? They likely have the same result onboard a boat.

The key point is a prudent boater would buy quality battery, as there is extensive evidence that "cheap" batteries can have poor construction/assembly, mismatched cells that increase likelihood of cell overvoltage and BMS that don't actually have safety features that they advertise. Unlike an electric scooter, car, etc..., we can't just step off onto the sidewalk when 300 NM from shore!

Has the OP selected a battery yet? I think that was the original question...

Thank you for supplying these scientific research articles. I did read a couple of them, they were interesting and informative. One caveat, apparently the scientific community uses LFP to mean LiFePO4 cells or Large Format Power cells, just a bit of a difference there.

I wonder if there is a LFP LFP?

 

[SteveHughessails]

How would we be able to identify a substandard battery or one that is housing an inadequate BMS?
Amazon reviews can be misleading

I read in an early post that Li Time has an issue they haven’t figured out yet or maybe it was they don’t know they have the issue yet?

 

[Hayden Watson]

The best way I know of is to look for tear-down videos to see how they are built. Will Prowse makes a lot of them.

 

[Screen Saver]

I know of one boat on a circumnavigation that damaged his very expensive Lithionics bank by charging with the

First, with two batteries you cannot improve on the diagonal wiring method from a circuit resistance point of view.

Second, you have missed what is actually occurring here.......

The circumnavigation boat you refer to doesn’t make sense Im sorry. AGM Damage starts a little before LifePo4. Most cruisers would not let their AGMS exceed anything like 15V, in the absolute worst case, and if they do they are shorting their life and damaging them This equates to 3.75V/cell in LifePo4 chemistry. The absolute Max for LifePo4 is about 4.2v and again at this level you will damage LifePo4. Typically, if we are considering the 99% for sure damage point worst case AGM is 15V LifePo4 is 16V But a regular charge to 3.75 on LifePo4 is unnecessary and not likely to cause long damage. Basically if he had AGMS they would have been killed also.
It is said for what its worth “For the 12 Volt Lithionics batteries, the HVC is set at 15.6 Volts
So yep if he reached that, then the problem was not due to using a conventional charger

I chose to disagree with what I understand is the Diagonal method (and for once Im not on my own)., but for one basic reason. Consider 3 batteries in parallel following the diagonal method, The middle battery due to resistance and cabling etc is very likely not going to get the same charge, or for hypothetical exaggerated example, consider the positive lead from the first battery had some corrosion in the lug or cable, the second and last battery would also suffer the reduced positive. Anyway you look at it the resistance drop and potential will have an impact. Now consider a star/buzz bar configuration. Again 3 battery example is easier to see. If each battery has the same length of leads, any connection type issues cannot effect the whole bank. I will try to attach AI's words for interest sake.

I have full control over my BMS’s and the only way this could happen in my environment is a setting called “overcharged bank “ and also “over charged cell” which in my case if triggered it would stay in that state until it reached “Over charge release” value. So perhaps in your case these values are not the same between batteries, or one cell in one battery is triggering this, so it disconnects and the other one with a different values, or no cell issues keeps going. When this happens, I would try letting it run on just one for some time and see if the disconnected one reconnects. I suspect it will eventually. This will sort of confirm my theory. If you have multiple external BMS’s you could clearly swap them to prove it’s the BMS setting or a battery cell. If you don’t then you definitely need to get some BMS software

 

[dlochner]

I chose to disagree with what I understand is the Diagonal method (and for once Im not on my own)., but for one basic reason. Consider 3 batteries in parallel following the diagonal method,

You are in good company, Victron has a primer on basic electrical systems and they note the diagonal panelling method is simple and effective, but not perfect. Sometimes we can't let the perfect be the enemy of good. In my own case, there just isn't room to use a busbar or posts to connect the batteries, so I have used the diagonal method to connect 3 LFP batteries.

https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

 

[Hayden Watson]

Here is a good explanation of the fire potential of LFP cells.

 

[Foswick]

Here is a good explanation of the fire potential of LFP cells.

Yes. He does ignore the fact that other form factors react slightly differently, but this video is all good information and representative of the actual risk profile of LFP chemistry. Importantly, he did not mention the fact that if one cell was compromised in this way, it will not cause neighboring cells to go into thermal runaway, which is the real danger with large multi-cell packs in other chemistries.

He was right to ignore overcharge events, for this demonstration, but those should not be disregarded, as they are a cause of fires with LFPs. But, these occur in packs with small/inadequate BMSs, usually for handheld tools and such, where small form factor and low price are key selectors. Importantly, if the BMS also monitors temperature, the risk of catastrophic failure is so low as to be negligible.

(I'm glad he also mentioned LTO - which is safer than even LFP. So, the obvious question is, "Why don't we use LTO, then?" The answer is that LTO has a much lower energy density than LFP. It is also quite a bit more expensive. Pretty much the only thing it brings to the table, for this application, is improved safety. And, when LFP is already more than safe enough, it just isn't seen as worth it.)

But ...

Following this thread leads me to an important piece of advice. This is not a good place to get advice on battery safety. There is too much misinformation mixed with good information - very confusing if you are trying to understand and make good decisions. There are some people who are giving good information, but there are some very convincing (and otherwise very knowledgeable) people giving bad information. You shouldn't trust anyone, including me.

And, unfortunately, marine electricians are kind of hit-and-miss as to whether they get it right. So, right now, there isn't a good place to turn to get reliable information. ABYC and USCG are at least 3-4 years behind and still make some generalizations that demonstrate a lack of understanding. That would seem like a good thing - being extra conservative - but until LFP is the norm and installations have become fairly standardized, there will still be some new-frontier aspect to every installation.

If you are not comfortable with that, on your boat, and cannot assess and manage the risk on your own without relying on an electrician that might or might not understand the technology, then the timing is probably not right for you to consider converting. We are still a bit in the wild west days, but getting closer to mainstream standardization.

I expect that about 5 years from now, we will see the standard solution is an LFP battery with a "smart" BMS, with temperature sensors, and a configurable onboard regulator to protect charging circuitry. So, the battery's firmware will be configured at installation time to negate the need for external protection for alternators and wiring. It will sense parallel configurations and manage appropriately.

This doesn't exist, currently, that I am aware of. But, I am sure it is coming. If I needed another project, I would start that company, except that there are dozens of other companies that are already working on it.

So, if that's the level of drop-in-edness that you need, then you'll have to wait a few years. But, even then, such a solution will not take full advantage of the capabilities of LFP to charge rapidly, if your charging circuitry (i.e. alternator) is not up to the task and/or the wiring from the alternator to the battery is in adequate. It will just protect your current system. To take full advantage will require other upgrades.

But, for most people, they just don't need that. Simply having higher energy density and a better life cycle is all they need.

 

[Johann]

The circumnavigation boat you refer to doesn’t make sense Im sorry. AGM Damage starts a little before LifePo4. Most cruisers would not let their AGMS exceed anything like 15V, in the absolute worst case, and if they do they are shorting their life and damaging them This equates to 3.75V/cell in LifePo4 chemistry. The absolute Max for LifePo4 is about 4.2v and again at this level you will damage LifePo4. Typically, if we are considering the 99% for sure damage point worst case AGM is 15V LifePo4 is 16V But a regular charge to 3.75 on LifePo4 is unnecessary and not likely to cause long damage. Basically if he had AGMS they would have been killed also.
It is said for what its worth “For the 12 Volt Lithionics batteries, the HVC is set at 15.6 Volts
So yep if he reached that, then the problem was not due to using a conventional charger

The LFP batteries were damaged by overcharging at a lower voltage. Years ago when LFP batteries where just beginning to be used in marine applications, there was not a lot of experience with long term use. Over the course of many years and many battery failures the voltage and charging recommendations changed. We also found out the mechanisms that contributed to the damage and degradation. The 4.2V maximum you state is the limit for immediate damage, but charging at lower voltage can also cause damage if the charge voltage continues after the cells are full. Anything over 3.42V has potential to degrade the cell. Once the anode is full of Lithium ions, continuing to apply a charge voltage causes Lithium metal to form on the anode. This reduces available Lithium, as well as reducing the area on the anode for intercalation. This is the reason more battery BMSs are including full charge protection, which disables the charge FETs when there is a charge voltage and low amps. Batteries were not retaining the warranted capacity for the warranty period.

The typical stock internally regulated Hitachi has a voltage setpoint of 14.5V +/-0.3V. So if you are running for hours and hours at 14V+ you are degrading your Lithium cells. But the cells may not degrade evenly and then that’s how you end up with cell imbalances that the passive balancers can’t correct. The Lithionics HVC is at 3.75V on any cell, or 14.8V pack voltage on my documents. Where did you get 15.6V? So in this case, after just a few years, it’s likely the cells had become damaged to the point that imbalances were causing a cell to exceed the HVC (3.75V), and the BMS disconnected. As I recall this was a BMS with a single contactor.

You can read some about LFP characteristics here:

Lithium battery systems | Nordkyn Design

nordkyndesign.com

I chose to disagree with what I understand is the Diagonal method (and for once Im not on my own)., but for one basic reason. Consider 3 batteries in parallel following the diagonal method, The middle battery due to resistance and cabling etc is very likely not going to get the same charge, or for hypothetical exaggerated example, consider the positive lead from the first battery had some corrosion in the lug or cable, the second and last battery would also suffer the reduced positive. Anyway you look at it the resistance drop and potential will have an impact. Now consider a star/buzz bar configuration. Again 3 battery example is easier to see. If each battery has the same length of leads, any connection type issues cannot effect the whole bank. I will try to attach AI's words for interest sake.

With just two batteries there is no difference in resistance. Also in practice three batteries may not be an issue due to the resistance of short 4/0 cable (0.05mΩ per foot) being much less than the internal resistance (IR)of the batteries. My middle battery has a lower IR than the outer two and thus contributes more, not less, despite the increased cable resistance. As far as corrosion or a bad connection, that should be checked for with an infrared temperature gun, regardless of configuration. Once past three or four batteries you might have issues with diagonal connections, and then you should wire as you have recommended in my opinion.

I have full control over my BMS’s and the only way this could happen in my environment is a setting called “overcharged bank “ and also “over charged cell” which in my case if triggered it would stay in that state until it reached “Over charge release” value. So perhaps in your case these values are not the same between batteries, or one cell in one battery is triggering this, so it disconnects and the other one with a different values, or no cell issues keeps going. When this happens, I would try letting it run on just one for some time and see if the disconnected one reconnects. I suspect it will eventually. This will sort of confirm my theory. If you have multiple external BMS’s you could clearly swap them to prove it’s the BMS setting or a battery cell. If you don’t then you definitely need to get some BMS software

It‘s not my case. The batteries in question are internal BMS models, two in parallel. But he seems to have solved the issue with a few cycles, so probably just balance issues on a new battery.

 

[Tally Ho]

I have been monitoring my new LFP batteries for a few months now. 2) 100 Ah LIFEPo4 smart batteries, My only real issue is that the 2 batteries generally don’t have the same SOC, except maybe after charging them independently at 14.6 volts (per mfg recommendation).

But despite the SOC issue, the batteries work well and typically share the house load just fine, and almost always have the same voltage . After a sail…


And today after sailing 3.5 hours…


I have yet to have any concerns about heat or fire with these batteries.

Greg

 

[Maine Sail]

How would we be able to identify a substandard battery or one that is housing an inadequate BMS?
Amazon reviews can be misleading

I read in an early post that Li Time has an issue they haven’t figured out yet or maybe it was they don’t know they have the issue yet?

The issue with Li-Time , Redodo, Powerqueen & others is the over charge protection they instituted about 18 months ago. Wattcycle has a fix rolling out soon but so far I have heard no solutions from Shenzen Lizutime..

 

[SteveHughessails]

The issue with Li-Time , Redodo, Powerqueen & others is the over charge protection they instituted about 18 months ago. Wattcycle has a fix rolling out soon but so far I have heard no solutions from Shenzen Lizutime..

Appreciate that. My 100Ah would have been before that but the blue tooth 50Ah we just bought would have the over charge concern then. Any recommendations? 14.4 max maybe shut it down at 90-95%?

 

[Maine Sail]

Appreciate that. My 100Ah would have been before that but the blue tooth 50Ah we just bought would have the over charge concern then. Any recommendations? 14.4 max maybe shut it down at 90-95%?

Bluetooth does not dictate whether or not it has overcharge protection. Any brand that has it, has it in both BT models and non-BT. Without knowing brand & model it is impossible to say. Unlike lead batts each LFP has its own computer inside it so brand/model are critical to know...