Lithium batteries

[Art]

I’m just starting to research swapping our 8D AGM’s for LFP’s.

Interesting looking products here.

https://www.custommarineproducts.com/lifepo4-marine-batteries.html

Built-in BMS which should allow drop-in replacements for most lead batteries with existing charging systems.

Those batts' stats read out very well. Unfortunately... For equivalent power availability... their cost is 8X my East Penn FLA deep cycle batts' cost. Last summer, I needed to put in a new house bank [4 - 31 deep cycle]. Cost: $440. The old batt bank was just over 9 yrs old and still working... at reduced capacity.

 

[Xsbank]

Stupidly expensive. Shows you how far the industry has to go yet.

 

[Andy G]

It`s a 10 yr old boat with under 750 hours on the Yanmar 315hp mains. Current owner has never showered on the boat, used it as a dayboat, says selling due to not using it. Bet he`s never run the aircon either. Boat has a "C Zone" electrical systems management system.

Bruce, you're not selling the mighty IG? Besides, you can't by a boat from an owner who never showers!

 

[twistedtree]

Those batts' stats read out very well. Unfortunately... For equivalent power availability... their cost is 8X my East Penn FLA deep cycle batts' cost. Last summer, I needed to put in a new house bank [4 - 31 deep cycle]. Cost: $440. The old batt bank was just over 9 yrs old and still working... at reduced capacity.

That's an impressively low cost for East Penn (Deka) groups 31 batteries. What is their Ah rating? I can't find any specs other than CCA and the like. The cheapest I can find Deka group 31s is around $140-$150 each. The 8x cost difference seems like a real stretch for equivalent usable ah capacity. I think the cost difference relative to FLA is really in the 4-5x range. And compared to AGMs it's in the 2-3x range. And that's dropping as we speak to less than 2x.


Here's a real cost comparison with products available today. Granted this is for a larger battery system, but it's still indicative. These are costs for the stock AGM battery system in my boat vs the LFP system I am installing.


Stock system: 10x Lifeline 8D AGMs. $670 each, for a total cost of $6700. Capacity at 24V is 1275 ah, with about 637 ah usable with 50% DOD cycling. That comes out to $10.50 per usable ah of storage.


LFP system: 6x MG Energy batteries. $3500 each for a total cost of $21,000. Add the BMS for another $1500 for a total of $22,500. Capacity is 280ah @ 24V per battery, so a total of 1680 ah, and it's all usable. Yes, it's a big battery system. That comes out to $13.40 per usable Ah, or a 29% increase over the cost of AGMs, and nothing even remotely close to 8X. To me, that's worth it in the blink of an eye.

 

[sunchaser]

Peter
No argument with your math. At some point battery system size, type and related costs need to be compared with the cost of fuel for an already installed diesel genset.

Thus, to satisfy my math a comparison was needed between battery size, type and capacity while considering genset, on engine alternators and solar. Then add in dock time Vs cruising hours. Then comes complexity, redundancy, simplicity and related hassle factors. Whew, almost overwhelming unless there is a strong commercial reason or a complicated new build occurring.

 

[twistedtree]

Peter
No argument with your math. At some point battery system size, type and related costs need to be compared with the cost of fuel for an already installed diesel genset.

Thus, to satisfy my math a comparison was needed between battery size, type and capacity while considering genset, on engine alternators and solar. Then add in dock time Vs cruising hours. Then comes complexity, redundancy, simplicity and related hassle factors. Whew, almost overwhelming unless there is a strong commercial reason or a complicated new build occurring.

I totally agree. And that's why you get to a tipping point where boats just run a generator 24x7. That seems to be in the 60-70' range.


I think one of the big driving factors to LFP for a lot of people is to have a quiet boat at night (no generator), but still have enough HVAC to keep a stateroom cool over night. I might get tempted by that when the time comes, but right now it's not a design objective for our boat. I still think there is a certain power level where it just makes more sense to fire up the generator. In general, HVAC is over that power level, however I have seen the latest variable speed chillers in operation in hot. steamy weather, and the power draw is remarkably modest. Back of the envelope, I could definitely run through the night on batteries. But my 12kw generator would do it too, and I doubt I would hear it over the sound from the air handlers.


I also think boats are being built now where the power systems are just too darn big for 24V. In all honesty, 200, or 300, or 400A flowing through wires and connections scares the crap out of me on a boat where there is so much opportunity for connection degradation. A lot of people have viewed LA batteries as the limiting factor for power system capacity, and that LFP now enables bigger systems. I tend to disagree, and feel it's DC voltage that is the limiting factor, and that we have really crossed the limit for 24V, no matter what king of battery.


I think the next big evolution will be going to high voltage DC. And I'm not talking about 48V. I'm talking about somewhere in the 100V to 300V range. That would bring current way down, and I think ultimately be much safer, even at the higher voltage.

 

[Art]

Quote:
Originally Posted by Art View Post
Those batts' stats read out very well. Unfortunately... For equivalent power availability... their cost is 8X my East Penn FLA deep cycle batts' cost. Last summer, I needed to put in a new house bank [4 - 31 deep cycle]. Cost: $440. The old batt bank was just over 9 yrs old and still working... at reduced capacity.

That's an impressively low cost for East Penn (Deka) groups 31 batteries. What is their Ah rating? I can't find any specs other than CCA and the like. The cheapest I can find Deka group 31s is around $140-$150 each. The 8x cost difference seems like a real stretch for equivalent usable ah capacity. I think the cost difference relative to FLA is really in the 4-5x range. And compared to AGMs it's in the 2-3x range. And that's dropping as we speak to less than 2x.

Regarding my quoted statement at top, in context to your quote inquiry:

For over a decade my only battery purchase shop has been our local "Batteries Plus Bulbs" outlet [we have plenty of car/truck/SUV vehicles, a few boats and an RV - BPB likes me as a customer; they treat me correctly].

East Penn manufactures most if not all BPB's marine and other vehicle batteries. For sure their FLA batts are East Penn... under a different label for sales reasons; e.g. in this marine deep cycle case, "Duracell". Punch up link.

https://www.batteriesplus.com/produ...ne-and-boat/deep-cycle/bci-group-31m/sli31mdc

In regard to the long battery review I recently read... four East Penn deep cycle FLA batteries [with 10% discount due to corporate promo reasons, as well as a touch of local store, good customer additional discount] cost me 8x less than the price of two of the other batts in the review... while both battery choices are providing similar ah capability. That said and in faieness.. the other two batts are a bit safer, over a period of years require a bit less maintenance and do charge a bit quicker.

I'm not saying that the other batts are not a really good battery choice in many ways, because they surly are. I'm just saying that I can power our live aboard Tollycraft boat's house bank for over 9 years at 8x less $$$ cost with FLAs. Just can't pass up that big of a $avings when capabilities of the other batts would not make our simple weekend [and occasional multi week] recreational boatlife [love to swim] any easier or more enjoyable.

Then... taking into account the many batts that power our other boats, cars, trucks, motor home etc. Well, you get my point! BPB's line of East Penn FLA batts = considerable cost savings with little effort and consistently available BPB outlets wherever we go.

 

[TDunn]

Most of the drop in lithium iron phosphate batteries I have seen are limited to a 100 amp discharge by their battery management system (BMS), so cranking a big diesel would require 4+ 100 Ah batteries in parallel. Some of those drop in replacement batteries limit how many you can put in parallel and many do not allow series connections. The limits on parallel and series connection are due to BMS design. At present it seems that lithium batteries are best suited to being house bank batteries while you maintain lead/acid batteries for engine starting. That means two separate charging systems.


As to cost, I just built a 10 kilowatt battery bank. I went flooded lead acid using 8 Grp 27 105 amp-hr batteries. The cost including tax, core charges and state recycling fees was $1,374.00. I have a nominal 5,040 usable watts based on a 50% depth of discharge. That will decrease at high discharge rates due to the Peukert effect. Had I gone with lithium Iron Phosphate batteries and equivalent system would have cost $6,013.60, or about 4.4 times the cost of lead acid batteries. That is the cost for six Battle Born 100 amp-hr batteries. I would need six batteries because I have a 24 volt system and have to buy batteries in pairs. I could use 24 volt batteries, but they would actually cost more than a 12 volt system. I also based the pricing on 80% depth of discharge for the lithium batteries although you can discharge lithium batteries to 100%, discharge to 100% definitely decreases cycle life for lithium iron phosphate batteries.

 

[O C Diver]

That's an impressively low cost for East Penn (Deka) groups 31 batteries. What is their Ah rating? I can't find any specs other than CCA and the like. The cheapest I can find Deka group 31s is around $140-$150 each. The 8x cost difference seems like a real stretch for equivalent usable ah capacity. I think the cost difference relative to FLA is really in the 4-5x range. And compared to AGMs it's in the 2-3x range. And that's dropping as we speak to less than 2x.


Here's a real cost comparison with products available today. Granted this is for a larger battery system, but it's still indicative. These are costs for the stock AGM battery system in my boat vs the LFP system I am installing.


Stock system: 10x Lifeline 8D AGMs. $670 each, for a total cost of $6700. Capacity at 24V is 1275 ah, with about 637 ah usable with 50% DOD cycling. That comes out to $10.50 per usable ah of storage.


LFP system: 6x MG Energy batteries. $3500 each for a total cost of $21,000. Add the BMS for another $1500 for a total of $22,500. Capacity is 280ah @ 24V per battery, so a total of 1680 ah, and it's all usable. Yes, it's a big battery system. That comes out to $13.40 per usable Ah, or a 29% increase over the cost of AGMs, and nothing even remotely close to 8X. To me, that's worth it in the blink of an eye.

As a comparison, my 8 Trojan T-105s with 880 ah (440 ah with a 50% DOD) cost around $800 from the golf cart refurb company on their spring special and no sales tax in Delaware. That's about $1.82 per per ah.

Ted

 

[twistedtree]

In regard to the long battery review I recently read... four East Penn deep cycle FLA batteries [with 10% discount due to corporate promo reasons, as well as a touch of local store, good customer additional discount] cost me 8x less than the price of two of the other batts in the review... while both battery choices are providing similar ah capability. That said and in faieness.. the other two batts are a bit safer, over a period of years require a bit less maintenance and do charge a bit quicker.

I think you are not accounting for the difference in usable capacity between LA and LFP. Working both hard, or as hard as is recommended by their manufacturers, you can use 50% of LA capacity, and 100% of LFP.


You 4 cell Duracell/East Penn is 420 ah @ 12V, 210Ah usable, and cost $440. The referenced LFP batteries, a 120ah 12V battery is just under $1100. Two of them would provide a bit more usable capacity (240ah vs 210ah), and cost $2200. That's 5x, not 8x, and actually a bit less considering the increased usable capacity of the LFP battery.


I'm not trying to argue they are cheap, but just trying to be sure they are being compared accurately. And if you prefer FLA or whatever reason, I have no problem with that either. No doubt that FLA is still the lowest cost per ah at initial purchase.

 

[twistedtree]

All the discussion so far has been around initial cost of different types of batteries. That's a very real consideration, but so is lifetime cost, and that's where LFP has a strong advantage.


If you are lucky, a typical FLA or AGM battery is good for 1000 cycles, and often a lot less. An LFP battery, even under the harshest operation, will yield 2000 cycles. And in the much less strenuous operation of a boat power system, 5000 cycles or more are projected.


With this taken into consideration, and even under the worst case yield of only 2000 cycles, LFP has a LOWER lifetime cost per Ah than AGM, and is getting pretty close to the lifetime cost of FLA.

 

[Art]

All the discussion so far has been around initial cost of different types of batteries. That's a very real consideration, but so is lifetime cost, and that's where LFP has a strong advantage.


If you are lucky, a typical FLA or AGM battery is good for 1000 cycles, and often a lot less. An LFP battery, even under the harshest operation, will yield 2000 cycles. And in the much less strenuous operation of a boat power system, 5000 cycles or more are projected.


With this taken into consideration, and even under the worst case yield of only 2000 cycles, LFP has a LOWER lifetime cost per Ah than AGM, and is getting pretty close to the lifetime cost of FLA.

Seems to me that after a decade of the same batteries being used has gone by... wouldn't it simply be wise to be ready to [to want to] refresh the entire batt system with new batts anyway?? Is it that the more expensive batts will last 20 yrs. or even 30 yrs. without manifesting problems or concerns of their own? Do we want 20 plus year old "non refreshed" batts of any sort in our boat? I do not know answer to these questions myself. What do others think?? Please provide any very long term battery experiences. I'm interested and feel sure others are to.

 

[Ka_sea_ta]

When I updated the DC system in our boat I did all the cost calculations of FLA, AGM, and Lifepo's. The cost per usable amp/hr calc at the time was about $2 for FLA, 4 for AGM and about $12 for LiFe. (100 amp/hr Battleborns were about 1k at the time and used 80% as the low SOC).... The batteries are just a part of the DC system, in order to take advantage of LifePos most charging systems have to updated to take advantage of their higher Charge current acceptance rate. If doing a complete DC system, LiFePo may be a good choice but to install in an existing DC system designed for FLAs the cost to take advantage of LI is a lot more then just the cost of the batteries.... to provide In my particular case I chose AGM's and kept my existing Alternators and Inverter/charger. I did add a 400 watt solar system for the float portion of the charge cycle..

 

[sunchaser]

A missing ingredient here is that utilizing new technology is in a boater's DNA. Whether TT, Delfin or whoever the learning curve for those who are less concerned by cost and more by battery innovation is a fun ride to follow. That innovation curiosity is why Tesla has done well and now much copied. The cars aren't cheap but they sure as heck are fun to drive and talk about.

TT has a cutting edge background and is carrying his philosophy and inquisitiveness into new areas. This permits us Walter Mittys to enjoy his ride and path.

 

[RickyD]

I'm been powering an off-grid house with LFP (one of the several different li-ion chemistries) for just about a year now. I love them, and would never use lead again for any sort of power system, including on a boat. The Nordhavn 68 that I'm building will have LFP as well, along with about a half dozen other Nordhavn's in recent production.


The most important thing to understand is that there are different types of Li batteries and they are VERY different from a safety perspective. They are different in other ways too, but the safety difference is the most important on for a boat. Everyone has heard about the 787 battery issue, Samsung phones, and various other Li battery fires. In those applications, including in cars, packing as much power as possible into the smallest space, and lightest weight is what it's all about. As a result, they all use so-called NMC or LFC chemistries. These are much higher power density, but also much more volatile.


LFP is a lower power density, and much more stable chemistry, and the only thing I would consider for use on a boat. There are numerous studies, tests, and videos of LFP batteries having nails drive through them, dead short circuits, flame throwers, etc. LFP batteries just smoulder and off-gas, where NMC and LFC batteries catch fire and take off in a cascading fire until there is nothing left. Which would you want on your boat? LFP is very stable, and I think actually less dangerous than lead.



But the reason I love them is because they just work much, much better than lead. They cost more, the premium is reducing quickly. My boat system, which will be a manufactured, fully engineered, packaged system, is only about 50% more $$ than equivalent usable capacity AGMs.



Why I like them:


- They don't off-gas one of the most explosive gasses on the planet.



- They aren't filled with one of the most highly corrosive acids on the planet.



They aren't filled with lead which is one of the most toxic materials on the planet.


- They don't heat up when used or when charged, assuming use comparable to how you would use a lead battery.


- They accept full charge current right up until they are full. There is no more long drawn out absorption stage that drags out charging time, and generator run time. Then end result is that you can recharge is about 75% of the time it takes to charge and equivalent lead battery, using the same charger(s). And they can typically accept higher charge currents, so can charge even faster if you want. With lead, increasing charge current produces significantly diminishing returns after a certain point. With LFP, a full recharge from empty to full can very reasonably be done in 2-3 hrs.


- They are much more efficient than lead. 98-99% vs 80-85%. So what goes in, come back out. This is particularly helpful if you are also using solar since you can capture and use that much more of the produced power.


- You can run them indefinitely at any state of charge. No more worries about draining them all the way down, or not fully recharging frequently enough or full enough.


But of course there are some down sides.


All batteries will be ruined if you over-discharge them, or over charge them. But with LFP, death is a bit more abrupt and certain. So where with lead you might be able to get away with a little slip up or two, chances are you would completely kill your LFP battery.


As a result, nearly all LFP batteries have protections built in to disconnect them just short of disaster. This is akin to a low voltage cutout that is incorporated in nearly every inverter to keep it from unintentionally flattening your batteries. In every way, the same protections would benefit lead batteries, but we don't use them. Largely because of the higher cost of LFP, they are common place.


Similarly, you need to be mindful of over charging, so need to be sure all your chargers are set so they will not over charge the batteries. It's typically not a big deal to do this, but you can't just blow it off or it could be a costly mistake.


But all this is good practice anyway, and shouldn't lead you to believe LFP is in any way fragile. It's just the opposite. Keep it within well understood limits, and they just work, day in and day out, with no fuss. Honestly, much LESS fuss than lead because you dopn't have to worry about leaving them at a low level for too long, or getting them fully recharged frequently enough. You can literally ignore them.


So to the OP's question, I don't believe anyone knows yet how long LFP will actually last in a boat application. There are lots of tests demonstrating 2000 cycles, but anything more than that is just extrapolation at this point. But keep in mind that 2000 cycles is probably 10 years on a boat, and that would be for a pretty heavily used boat that is going through a full battery discharge/charge cycle 200 days per year. I'll bet few if any of us come even close to that.


For the particular boat you are looking at, the first and most important thing I would check is what chemistry the batteries are. If they are LFP, I would just happily use them. If they are something else, I would probably plan on replacing them, just for safety reasons.

Alright, someone who really knows Li batteries. I'd love to add them to my boat so I can pick up some more house bank capacity but they may not have the cranking power I need for starting my Cat 3208s. I'd prefer to have all of my batteries the same.

 

[noxidg]

Hi, Enerdrive are a Queensland company based at Wynnum, I’m guessing the batteries wouldn’t be anymore than 2 years old

 

[O C Diver]

All the discussion so far has been around initial cost of different types of batteries. That's a very real consideration, but so is lifetime cost, and that's where LFP has a strong advantage.


If you are lucky, a typical FLA or AGM battery is good for 1000 cycles, and often a lot less. An LFP battery, even under the harshest operation, will yield 2000 cycles. And in the much less strenuous operation of a boat power system, 5000 cycles or more are projected.


With this taken into consideration, and even under the worst case yield of only 2000 cycles, LFP has a LOWER lifetime cost per Ah than AGM, and is getting pretty close to the lifetime cost of FLA.

I can see your argument relative to commercial use where the application drains the batteries between 50 and 80% daily. However, for many, most of us, the cycle life is unattainable. Further, does anyone truly believe that their battery bank will last 10 to 15 years with our type of use? I can see where a high charge rate for both Li and Firefly batteries can be a big advantage, but from a value of cycles standpoint, most of us will never realize it.

The last part of the equation is premature failure. In 5 years, if your Li fails either as your fault or otherwise, how upset will you be? My experience with batteries past the warranty period has been mixed, so I tend to focus on the value relative to the warranty period.

Ted

 

[BruceK]

Hi, Enerdrive are a Queensland company based at Wynnum, I’m guessing the batteries wouldn’t be anymore than 2 years old

If I add some more info,the current owner of 3 years did not fit them and thinks they are original to the 10yo boat. The PO to him was in Victoria, a dentist with a love of electronics. I`ve not yet seen the boat, but owner says it`s full of electronic stuff, and thinks it was built as a demo of state of art electronics as well as the Sydney 2010 Boat Show exhibit.

 

[goboatnow]

Yep, LFP’s are definitely more costly but here’s another consideration, as I sit here in Zihuatanjeo in 90’ weather.

Here our freezer runs nearly continuously, that coupled with house loads gets us to at 25 amp draw / hour at 12V.

From 4pm until 9am we’re not generating appreciable solar power, so about 15 hours of draw = 350-400ah’s to replenish the next day.

We have an 1025ah AGM bank. It accepts 100amps during bulk charge, Absorption acceptance starts at 80 and drops down to ~50. It takes a long time to get the house bank to 100% with a very lightly loaded genset running 5-6 hours. That sucks! We rarely get up to 100% as our solar is only good enough to keep up with loads and net an extra 10-15amps - no bueno for AGM’s.

Key benefit I see to LFP’s is reduced charge times with near linear charge acceptance. Huge advantage from where I sit, sipping a margarita.

Quiet boat with nothing running, that’s just not something you can put a price tag on in my opinion.

 

[twistedtree]

Alright, someone who really knows Li batteries. I'd love to add them to my boat so I can pick up some more house bank capacity but they may not have the cranking power I need for starting my Cat 3208s. I'd prefer to have all of my batteries the same.

The whole start battery question is an interesting one. A large enough LFP bank should have no trouble starting an engine. They actually can deliver 5C or more (500A for a 100ah battery) for short duration, so in some sense better for starting than LA. However many BMS manufacturers cap the current draw at the max sustained current which is typically more like 1C, presumably so they are more likely to make it through the warranty period.


On our boat I have kept LA for the start batteries, and done it for two reasons. First is so I don't have to worry about the surge current to start an engine. LFP might work fine. In fact it would almost certainly work fine. But I wasn't comfortable building a system that depended on it working fine.


The second is to have a backup in case the LFP shirts the bed. I've got an Off, Bank 1, Bank 2 battery switch so if the LFP craps I can easily parallel in one of the start banks (there are two of them, split between main wing, and two generators) and keep going. Loss of 24V (or 12V) on a boat would be startling, at a minimum. That would get me back on line quickly, and I could run indefinitely like that, though with minimal storage capacity and consequential need to run a generator most of the time if not on shore power or underway on the main engine.


I've gained a lot of confidence in LFP via the off-grid house project, but a boat needs a backup for everything, no matter how reliable.

 

[twistedtree]

Yep, LFP’s are definitely more costly but here’s another consideration, as I sit here in Zihuatanjeo in 90’ weather.

Here our freezer runs nearly continuously, that coupled with house loads gets us to at 25 amp draw / hour at 12V.

From 4pm until 9am we’re not generating appreciable solar power, so about 15 hours of draw = 350-400ah’s to replenish the next day.

We have an 1025ah AGM bank. It accepts 100amps during bulk charge, Absorption acceptance starts at 80 and drops down to ~50. It takes a long time to get the house bank to 100% with a very lightly loaded genset running 5-6 hours. That sucks! We rarely get up to 100% as our solar is only good enough to keep up with loads and net an extra 10-15amps - no bueno for AGM’s.

Key benefit I see to LFP’s is reduced charge times with near linear charge acceptance. Huge advantage from where I sit, sipping a margarita.

Quiet boat with nothing running, that’s just not something you can put a price tag on in my opinion.

To me at least, that's the #1 reason why I love LFP. Quick recharge times. And it's not because I'm putting more current into them. It's because they accept all I've got, all the time, until full. In contrast, LA chokes, barfs, and gurgles for hours until full. LFP is just a much, much better match to use on a cruising boat. I expect to be able to recharge mine in 2hrs, from empty to full. With LA, that would be a 6 hrs generator run.

 

[twistedtree]

Just a quick thought on BMSs (Battery Management Systems).


LFP systems all have one of some sort, but I think a lot of people hear that and imagine a computer that is managing some delicate balance between normal operation and disaster. Reality couldn't be further from that.


Most, if not all of what a BMS does is monitoring. And most of it is to protect you from doing something damaging to your batteries - something we are all free to do to our LA batteries, and have surely all done at one time or another. But because LFP has been expensive, and still is in a declining degree, much of what a BMS does is economic protection, not safety protection. It's saving you from the cost of forking up.


In reality, what a BMS does is just sit around and watch your batteries. It doesn't actually DO anything. It just watches. If anything starts to go wrong, it warns you. And if things start to go really wrong to the point where your batteries might get damaged, it will pull the plug. But that's really drastic action, and won't happen unless things go really wrong.


In reality, all you need to do is set your chargers to not overcharge (same as you do for LA). And make sure your loads can't drain the batteries dead (something we only partially do with LA). With that in place, your BMS will do exactly nothing - but monitor. My off grid system has been running for just about a year now, and so far the BMS has not done a single thing, other than watch, measure, monitor, and report. The batteries charge, discharge, recharge, and there is no fuss. It couldn't be more uneventful. I spend zero time tending my batteries now, where I used to spend a measurable amount of time before on my LA bank watering, checking, monitoring, equalizing, etc.


All that said, there is something that many BMSes do, and that's cell balancing. As part of monitoring, they watch for cells in series where one cell is reaching full charge sooner or later than others, and it boosts or drains the cell to bring it back in line with the others. This is where I think a lot of people imagine lots of on-going active management of your battery. But this is actually a very small activity. My BMS does not have any automatic balancing, and so far a year in, no balancing has been required. I also have a confession to make. I have NEVER balanced by batteries. They came from the manufacturer all at equal charge, so for kicks I decided to just go for it and put them into service. Now, a year in, they still don't require balancing.

 

[mvweebles]

I am undergoing a total rewire. Like TT, I chose LFP for house bank (700ah) and AGM for engine start, plus AGM for Gen and thruster (TT I'm sure has hydraulics). Despite the cost, this was a no-brainer for me. LFP are smaller, lighter, and have a very long lifespan so I can tuck them in an out of the way place. Which adds up to regaining a ton of space in my ER where I needed to be able to regularly service the T-105s. To round out the system, I have 800w of solar charging, a Magnum 3200 hybrid inverter, and a balmar 180A externally regulated alternator plus a second smaller Balmar for charging the AGMs.

I understand the case for Fireflies, though still not for me. I do not understand the case for FLA unless you're flipping the boat for resale. Only benefit I see is low initial outlay.

 

[noxidg]

Bruce,
If you can get the serial number from the battery or any Enerdrive component connect to it they will be able to tell you exactly when it was built and fitted as they are made to order
Geoff

 

[ranger58sb]

I’m just starting to research swapping our 8D AGM’s for LFP’s.

Interesting looking products here.

https://www.custommarineproducts.com/lifepo4-marine-batteries.html

Built-in BMS which should allow drop-in replacements for most lead batteries with existing charging systems.

I wonder what kind of cranking amps those offer...

Alright, someone who really knows Li batteries. I'd love to add them to my boat so I can pick up some more house bank capacity but they may not have the cranking power I need for starting my Cat 3208s. I'd prefer to have all of my batteries the same.

The whole start battery question is an interesting one. A large enough LFP bank should have no trouble starting an engine. They actually can deliver 5C or more (500A for a 100ah battery) for short duration, so in some sense better for starting than LA. However many BMS manufacturers cap the current draw at the max sustained current which is typically more like 1C, presumably so they are more likely to make it through the warranty period.

On our boat I have kept LA for the start batteries, and done it for two reasons. First is so I don't have to worry about the surge current to start an engine. LFP might work fine. In fact it would almost certainly work fine. But I wasn't comfortable building a system that depended on it working fine.

Thanks, TT, for speaking further to the start battery issue.

We have dual-purpose start/house banks, way more expensive to change that than it'd be worth... we transitioned to AGM starting in 2006... and I've mostly just increased capacity to the extent possible in the available space.

But one bank is probably approaching end of life, and I've been debating (with myself) whether to replace with the same Odysseys we have now (300 Ah total), Lifeline 12V AGMs (375 Ah), or Firefly Oasis Carbon Foam AGMs (348 Ah). I've mostly been ignoring LFPs, but then with this thread I began to wonder if maybe now would be the time to begin thinking more about an LPF option for this purpose. Sounds like not; or maybe the nuanced version of that is maybe OK but with more risk than I'm happy with.

I know I need 1250 CCA and 1560 MCA and I know I can get there with any of my three choices... although reserve declines if I move to either Lifeline or especially to Firefly. Still, eliminating LFP means the rest of my decision process is likely just some capacity/$$$ math.

-Chris

 

[sunchaser]

I do not understand the case for FLA unless you're flipping the boat for resale. Only benefit I see is low initial outlay.

One case for sure, most of us have boats that are recreational toys thus base our optional expenditures and changes upon need. House, cars, travel, gifts, art, philanthropy, investments and family all conspire to compete for dollars.

FLAs work good enough for +99% of us. But, like TVs LFP price decreases and ever increasing design improvements may some day sway more of the recreational boating fraternity.

 

[twistedtree]

There is another dimension to LFP that has only been touched on in passing, and it can be a distinct down side, if not a deal killer for some boats. That's temperature.


All batteries perform best at room temp, and all suffer in one way or another in high and low temps. LFP is not different, but the problems are more severe.


First, you don't want to let them go below freezing. If you try to charge them at a normal rate, you will damage them. And they don't store well much below freezing. So if you have a boat that gets laid up in the winter, the batteries will have to be protected from freezing, or removed and stored in a temp controlled space. And even f you boat isn't laid up but is subject to freezing, you will similarly need to protect the batteries from cold. I leave the heat on in my boat, so it's not an issue, or at least a manageable one.


Second, they don't like to be hot, and will age faster if operated over about 30C. This means that an engine room is typically not a happy place for LFP batteries. Unfortunately, a lot of boats have their house bank located in the ER, and they would have to be relocated if converting to LFP.

 

[ranger58sb]

First, you don't want to let them go below freezing. If you try to charge them at a normal rate, you will damage them. And they don't store well much below freezing. So if you have a boat that gets laid up in the winter, the batteries will have to be protected from freezing, or removed and stored in a temp controlled space. And even f you boat isn't laid up but is subject to freezing, you will similarly need to protect the batteries from cold. I leave the heat on in my boat, so it's not an issue, or at least a manageable one.

Second, they don't like to be hot, and will age faster if operated over about 30C. This means that an engine room is typically not a happy place for LFP batteries. Unfortunately, a lot of boats have their house bank located in the ER, and they would have to be relocated if converting to LFP.

Both of those would impact us. Additional reasons why LFP wouldn't be a great avenue for this boat at this time.

-Chris

 

[Ka_sea_ta]

Yep, LFP’s are definitely more costly but here’s another consideration, as I sit here in Zihuatanjeo in 90’ weather.

Here our freezer runs nearly continuously, that coupled with house loads gets us to at 25 amp draw / hour at 12V.

From 4pm until 9am we’re not generating appreciable solar power, so about 15 hours of draw = 350-400ah’s to replenish the next day.

We have an 1025ah AGM bank. It accepts 100amps during bulk charge, Absorption acceptance starts at 80 and drops down to ~50. It takes a long time to get the house bank to 100% with a very lightly loaded genset running 5-6 hours. That sucks! We rarely get up to 100% as our solar is only good enough to keep up with loads and net an extra 10-15amps - no bueno for AGM’s.

Key benefit I see to LFP’s is reduced charge times with near linear charge acceptance. Huge advantage from where I sit, sipping a margarita.

Quiet boat with nothing running, that’s just not something you can put a price tag on in my opinion.

You may want to optimize your charging system for AGM's the minimum bulk charge current recommended by Lifeline is .2c and anything less will increase sulfation... Lifeline Batteries can handle up to 5c if temperature compensated so in theory you could charge your bank 5k amps.... Big capacity battery banks are a great and wonderful thing but the batteries are just a part of the whole DC system your charging system has to sized correctly also.... most aren't...

 

[Jon H]

"I think the next big evolution will be going to high voltage DC. And I'm not talking about 48V. I'm talking about somewhere in the 100V to 300V range. That would bring current way down, and I think ultimately be much safer, even at the higher voltage."

My fathers boat, former USN WWII subchaser, has a 120+ VDC battery bank.

He uses regular household LED light bulbs for lighting using 120 DC power.
The items that require 120 AC are powered off the invertor, everything else
is 12VDC.

Underway charging is via a shaft generator (not practical for most yachts).

At anchor the boat can go several days without charging as the house load is rather small - no A/C system, etc.

Maybe a 120 VDC system (or bigger) is something to consider...….