Carbon Foam Batteries 1 Year Later

[Gordon J]

CMS,

Thanks. I am installing a new Magnum charger this week, but am still wondering about voltage sensitivity. I recently had a battery isolator go out and my new AGMs briefly saw 17 volts. Still have not tested to see how badly damaged. I doubt lead acid would have been damaged (and perhaps my AGM are not either), but thought it worth asking about voltage sensitivity. I'llb e stesting my batteries in a few days to learn whether batteries are toast.

Gordon

 

[Art]

Number of cycles and how deep always drives a batteries decline. The Firefly has a design cycle life of 1000 cycles to 80% DOD and 3600 cycles to 50%. The carbon foam makes this possible. The carbon foam limits and minimizes the sulfate from hardening and clustering something that murders other batteries when PSOC cycled.

QUOTE]

CMS - " design cycle life " mentioned in your above.

Is that computer design only? Have several randomly chosen Firefly batteries been hands-on tested, utilizing normalized marine conditions, to prove their ability that they can actually reach these stated levels of 1000 cycles for 80% DOD and 3600 cycles for 50% DOD?

 

[O C Diver]

I may have missed it, but the maximum draw down rate I saw on the spec sheet was 30 amps. What is the maximum draw down rate? It's not uncommon for me to see a 200+ amp discharge rate for maybe a half hour when making dinner with the microwave through the inverter. Wondering how that type of battery handles heavy discharges for 30 minutes

Ted

 

[sdowney717]

If you don't have temp compensation for all charge sources, can set absorption to 14.4V and float to 13.2V (float at 13.2V is very important) then I would not suggest buying Firefly batteries.

Not having the right charger, does this mean FireFly batteries will be ruined sooner?

 

[CMS]

I may have missed it, but the maximum draw down rate I saw on the spec sheet was 30 amps. What is the maximum draw down rate? It's not uncommon for me to see a 200+ amp discharge rate for maybe a half hour when making dinner with the microwave through the inverter. Wondering how that type of battery handles heavy discharges for 30 minutes

Ted

Ted,

What you saw is not a maximum discharge rate it is differing rates of discharge to 1.75VPC (10.5V) and how many Ah's it will net you from the battery. A 3 hour discharge rate would be 30.5A and net you 91.5Ah's before the battery hit 10.5V. A 10 hour discharge rate would be 11A and would net you 110Ah and a 20 hour discharge rate would be 5.8A and net you 116Ah of capacity. These are not the maximum discharge rates. A 200A load on a FF bank that is sized for that is not even breaking a sweat.....

Not having the right charger, does this mean FireFly batteries will be ruined sooner?

Absolutely and this goes for all VRLA batteries. 14.4V max (temp compensated) and 13.2V max float. they prefer the battery not to float at all but realize quiescent loads exist.

 

[FoxtrotCharlie]

Wow, 65 posts - and no one has even said the word 'anchor'

 

[TDunn]

Those Firefly batteries are really expensive. I run four Everstart GRP 29 deep cycle batteries (made by Johnson Controls). They are rated at 115 amp-hours, so at 50% discharge I have 230 amp hours available. The cost for the four batteries is $348. Three Firefly batteries would give me about the same available amp-hours at a cost of $1,458. The Firefly batteries would have to last more than 4 times as long to make them worth while. Frankly the cost simply isn't justified from my point of view, particularly since my solar panels keep my batteries near 100% capacity.

 

[Art]

CMS

I'm looking forward to learn input to my questions on post # 62

 

[dhays]

Those Firefly batteries are really expensive. I run four Everstart GRP 29 deep cycle batteries (made by Johnson Controls). They are rated at 115 amp-hours, so at 50% discharge I have 230 amp hours available. The cost for the four batteries is $348. Three Firefly batteries would give me about the same available amp-hours at a cost of $1,458. The Firefly batteries would have to last more than 4 times as long to make them worth while. Frankly the cost simply isn't justified from my point of view, particularly since my solar panels keep my batteries near 100% capacity.

As has been pointed out, the cost/benefit analysis depends entirely on your use. Your use determines what your point of view is. If you deeply discharge your bank on a regular basis, you might be better off with the Firefly. ie they could easily last more than 4 times longer than LA. If you don't deeply discharge your batteries and your solar can readily get them back to 100% then likely the LA are your best option.

The other issues may or may not be of value, ie increased absorption rate, no watering, length of time between that they may sit at partial state of charge, etc....

I think they sound great for certain uses but not all. If I can solve the watering issue, I am thinking that for most of my use a simple Golf cart bank may be best for me. That may change however when I get more free time and can do more than weekends and the occasional week cruise.

 

[dhays]

CMS

I'm looking forward to learn input to my questions on post # 62

His post #32 has some very good information and a fair amount of informed anecdotal testimony that relates to your question.

 

[CMS]

Number of cycles and how deep always drives a batteries decline. The Firefly has a design cycle life of 1000 cycles to 80% DOD and 3600 cycles to 50%. The carbon foam makes this possible. The carbon foam limits and minimizes the sulfate from hardening and clustering something that murders other batteries when PSOC cycled.

QUOTE]

CMS - " design cycle life " mentioned in your above.

Is that computer design only? Have several randomly chosen Firefly batteries been hands-on tested, utilizing normalized marine conditions, to prove their ability that they can actually reach these stated levels of 1000 cycles for 80% DOD and 3600 cycles for 50% DOD?

It is not just computer design. They run then look at various tests, various temps, various discharge rates and then project design life using industry accepted calculations to arrive at DOD to cycle life under "ideal" conditions.

This is no different than how other manufacturers do it Firefly just calls it "design cycle life" and some other battery makers insinuate they have tested all batteries at all SOC depths for cycle life. This would take eons to do, tie up millions of dollars of test equipment etc. and it is not done. Almost all cycle life graphs are projected. While based on actual testing they are still using mathematical projections. Sadly ideal conditions do not exist in the real world. This is why I created my own PSOC test when the Firefly was shown to me. I'm a skeptic at heart...

While short in duration (data collection actually took over 6 months) this PSOC testing was enough to see marked differences in PSOC performance and cycle life degradation. Now if we could only get the industry to adopt a similar test we'd all have significantly better data with which to buy batteries.

The Firefly batteries have undergone numerous tests both independent and in their own lab. One test took a FF to 100% DOD (0% SOC) each cycle at a 1C discharge rate (116A for a 116Ah battery) at 25°C/77°F and it survived this 1250 times before falling to 80% of its original capacity.

In an independent J2185 Test, which is at 50°C/122°F, the Firefly ran for 724 cycles at 50% DOD. This is pretty insane at 122°F when you consider that a rise of just 10°F beyond 77°F can halve the cycle life of a lead acid battery.

The Firefly delivered a cumulative 35,108 Ah's and the Odyssey Group 31 PC2150 TPPL AGM, (another very good AGM) delivered just 7815 Ah's. This is actually pretty respectable at those temps. In that same test a Deka G-31 flooded battery delivered just 3264 cumulative Ah's.

Manufacturer claims on cycle life almost never stack up in the marine market because no one tests for PSOC capability, how many of us use batteries, nor do they all use the same test criteria. Lab data is really only sort of telling within a brand. For example if Trojan suggests that the T105 will do 1200 cycles to 50% DOD and the SCS-225 (group 31) will only do 600 cycles to 50% that is decent information within the Trojan line up. If Deka says their G-31 flooded will do 350 cycles and their golf cart battery will do 1000 cycles that too is good data within the Deka brand under ideal lab conditions...

Some outside the battery industry have been pushing BCI to initiate PSOC ratings to make it fairer to understand how a battery might fair in the real world of off-grid, RV or marine applications. Sadly the industry fights this tooth and nail.

So yes, this is why I said "design cycle life". From what I have seen I still suspect that in a PSOC application the cycle life of the Firefly should be considerably better than other AGM batteries. Also I don't think most realize how many cycles 1000 really is, it is a LOT. I have been working my LiFePO4 battery really hard for nearly 5 years and still have not broken 800 cycles to 80% DOD and I am regularly cycling it to 80% DOD in the off season...

 

[Art]

Some outside the battery industry have been pushing BCI to initiate PSOC ratings to make it fairer to understand how a battery might fair in the real world of off-grid, RV or marine applications. Sadly the industry fights this tooth and nail.

So yes, this is why I said "design cycle life". From what I have seen I still suspect that in a PSOC application the cycle life of the Firefly should be considerably better than other AGM batteries. Also I don't think most realize how many cycles 1000 really is, it is a LOT. I have been working my LiFePO4 battery really hard for nearly 5 years and still have not broken 800 cycles to 80% DOD and I am regularly cycling it to 80% DOD in the off season...

Thank you for comprehensive answer! - Art

 

[BandB]

Although we don't fit their true targeted customer, we still have them and we'll report back how we like them, but the very nature of this says that will be years from now. That's one of the problems in evaluating them that you have to go to the length of their usable lives and that takes years. Until you have a lot of batteries used like that then you live with the anecdotal evidence of just a few. Nothing wrong or bad about that, just the way it is. It's a bit like buying the first of a new car model and the day you drive it home you're asked how you like it. Of course, you love it then. The real answer has to come much later though.

Now, our reasons. Chargers are a pain. I don't care if you're hooked up at a marina or running them off your generator, I consider them a weak link and a source of potential problems, especially when no one is there to observe them. So, when not in use, we feel like we can let the batteries run down rather than leaving them on charge. How many threads to we have here where people return to the marina to find the charger has fried their batteries? It's just a little experiment. Worst case they get slightly longer life than other batteries. Best case they're trouble free for significantly longer and we get longer charger life. Our first test of them was to discharge them to about 25% and just see how they responded.

 

[Art]

Although we don't fit their true targeted customer, we still have them and we'll report back how we like them, but the very nature of this says that will be years from now. That's one of the problems in evaluating them that you have to go to the length of their usable lives and that takes years. Until you have a lot of batteries used like that then you live with the anecdotal evidence of just a few. Nothing wrong or bad about that, just the way it is. It's a bit like buying the first of a new car model and the day you drive it home you're asked how you like it. Of course, you love it then. The real answer has to come much later though.

Now, our reasons. Chargers are a pain. I don't care if you're hooked up at a marina or running them off your generator, I consider them a weak link and a source of potential problems, especially when no one is there to observe them. So, when not in use, we feel like we can let the batteries run down rather than leaving them on charge. How many threads to we have here where people return to the marina to find the charger has fried their batteries? It's just a little experiment. Worst case they get slightly longer life than other batteries. Best case they're trouble free for significantly longer and we get longer charger life. Our first test of them was to discharge them to about 25% and just see how they responded.

Regarding chargers - left on at dock when away: I never leave my boat plugged into dock and isolate all batts with perko switches before leaving. Soon as I'm back at dock I plug in and flip charger on. By time we leave batts are usually near or full charged. As we motor along they continue charge. We sometimes leave boat idle for up to three months. By multi meter hooked directly into batt bank... I've not seen our Deep Cell East Penn 31 T LA batts go down below 65% charge due to sitting isolated... usually they remain in low 70%'s

 

[ranger58sb]

How many threads to we have here where people return to the marina to find the charger has fried their batteries?

That's probably a fair point, but I can anecdotally remember many, many (many) of those eventually pointing toward old, "dumb," ferro-resonant chargers.

And the usual advice for the frie-ee is to get a 3-stage "smart" charger.

And then that thread usually peters off into oblivion... until the next one.

-Chris

 

[BandB]

That's probably a fair point, but I can anecdotally remember many, many (many) of those eventually pointing toward old, "dumb," ferro-resonant chargers.

And the usual advice for the frie-ee is to get a 3-stage "smart" charger.

And then that thread usually peters off into oblivion... until the next one.

-Chris

I have a good friend who is a boat or as they call it yacht manager, but most of the boats he manages are just very ordinary boats, even some Boston Whalers. However, he constantly gets called to do something by a new customer or a broker, goes to the boat and the charger and batteries are a disaster. A lot of it is just builders cutting corners and the owner continues with much like they came with. It's like taking a lousy charger that is suspected of cooking batteries and getting it rebuilt.

This area has been such an awakening to me. In over 30 years on the lake, I never used a charger on my boat, occasionally would let someone else use one I had.

 

[O C Diver]

Ted,

What you saw is not a maximum discharge rate...

A 200A load on a FF bank that is sized for that is not even breaking a sweat.....

Ok, so what is the maximum draw rate for 30 minutes per FF group 31 battery? As many of us have inverters for things like microwaves, how many group 31 batteries does it take to reasonably handle a 30 minute 200 amp load? Or were you saying, one group 31 battery can handle a 200 amp 30 minute load?

Ted

 

[sdowney717]

Absolutely and this goes for all VRLA batteries. 14.4V max (temp compensated) and 13.2V max float. they prefer the battery not to float at all but realize quiescent loads exist.

Interesting the max of 14.4volts.
Question is, what is the max volts coming from an engine alternator?
I have seen a big range over the years, and seem to recall mine is 14.4 to 14.7
Would engine run time with the alternator putting out too high the volts be a cause for concern?
My float voltage from the charger is set to 13.7 for my flooded cells. I can adjust it higher or lower.

Alternator & Charging System Checks (Alternator Testing)

ALTERNATOR CHARGING VOLTAGE

Most alternators that are charging properly should produce a voltage of about 13.8 to 14.2 volts at idle with the lights and accessories off. Always refer to the vehicle manufacturer's specifications. Many Asian vehicles, for example, have higher charging voltages of around 15 volts.

When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage.

The exact charging voltage will vary according to the battery's state of charge, the load on the vehicle's electrical system, and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.9 to 15.1 volts at 77 degrees F. But at 20 degrees F. below zero, the charging voltage might jump as high as 14.9 to 15.8 volts for a short period of time. On a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts.

 

[FF]

What usually kills boat batts is sitting for days at only partial charge , and almost never getting to 100% on the recharge.

This would be very difficult to create a test for.

Almost every batt style does well if discharged and i then quickly recharged to 100%

 

[ranger58sb]

What usually kills boat batts is sitting for days at only partial charge , and almost never getting to 100% on the recharge.

This would be very difficult to create a test for.

Almost every batt style does well if discharged and i then quickly recharged to 100%

And apparently many cruisers can't get there (quickly recharged) from here.

Hence one reason driving Carbon Foam AGM development.

And hence testing by CMS, Nigel Calder, et al.

-Chris

 

[Trundlebug]

But these carbon batteries aren't any better than Lithiums are they?

Do they recharge quicker? - No
Do they last longer - probably not, maybe about the same
Can they take deeper DOD than Lithium? - No
Are they lighter weight than Lithium? - No
Are they cheaper than Lithium? - probably about the same

So where is the advantage? It's easy to compare with flooded wet cells, yes they're much better. But so are Lithiums - and they are proven technology, coming down in price as their use increases in automotive applications and Mr Musks new Gigafactory comes online. I think you're all looking in the wrong direction...

 

[twistedtree]

Thanks, CMS. Your long reply a few posts back was very helpful.

It seems to me that the fundamental characteristics of CF batteries are the same as AGMs except for their greater immunity to sulfation. And you of course have emphasized the importance of this feature for many cruisers. Many (perhaps most) batteries don't wear out - they get trashed by their usage pattern.

You have also emphasized the importance of matching the battery to the boat and planned usage. I couldn't agree more.

Regarding AGMs, how often would you say they need to be returned to full charge to prevent sulfation? I'm thinking once a week? For many trawler owners, e.g. this forum, I think that happens reliably. Your batteries will return to full charge if you:

1) Plug into shore power overnight, or

2) Motor during the day long enough to fully recharge.

This of course assumes you have good charging equipment that can accomplish the recharge. But if you don't, I'd argue the problem is your charging, not your batteries.

I expect it's very rare for a motor cruiser to be at anchor without getting underway for more than a week, and that's the only time I see batteries experiencing sustained PSOC.

I can definitely see how on a sailing boat extended PSOC can and will occur since they are much less likely to get a full recharge while underway like a motor cruiser will. For them, the FF batteries sound like a worthwhile premium. And if a motor cruiser's engine alternator system can't fully recharge the batteries over the course of a typical session underway, and you don't return to shore power at least once a week, then they probably make sense in that application too.

 

[sdowney717]

But these carbon batteries aren't any better than Lithiums are they?

Do they recharge quicker? - No
Do they last longer - probably not, maybe about the same
Can they take deeper DOD than Lithium? - No
Are they lighter weight than Lithium? - No
Are they cheaper than Lithium? - probably about the same

So where is the advantage? It's easy to compare with flooded wet cells, yes they're much better. But so are Lithiums - and they are proven technology, coming down in price as their use increases in automotive applications and Mr Musks new Gigafactory comes online. I think you're all looking in the wrong direction...

Lots of work going into magnesium batteries, and have had some breakthroughs, just not yet there. I think it will happen. Lots more magnesium around than Lithium.
Magnesium To Replace Lithium-ion Batteries Soon | OilPrice.com

When and if they get it, Lithium demand will plummet, but consumers of DC power will be very happy.

Researchers at Toyota have discovered a new electrode for magnesium batteries
http://www.electrochem.org/redcat-blog/breakthrough-magnesium-batteries/

Toyota is of course an innovative car company, so their goal is to use magnesium not lithium batteries. Lithium supplies are limited.

http://techxplore.com/news/2016-05-toyota-scientists-breakthrough-safer-smarter.html

 

[CMS]

Interesting the max of 14.4volts.
Question is, what is the max volts coming from an engine alternator?
I have seen a big range over the years, and seem to recall mine is 14.4 to 14.7
Would engine run time with the alternator putting out too high the volts be a cause for concern?
My float voltage from the charger is set to 13.7 for my flooded cells. I can adjust it higher or lower.

Standard automotive type regulation (fixed voltage or thermistor manipulated) is simply a poor fit for any GEL or AGM battery not just Firefly. If moving to GEL or AGM the best solution is to design it as a system which includes the ability to program the correct absorption & float voltages, proper absorption duration, alternator temp compensation, proper belts to drive the loads, battery temp compensation from all charge sources, move the batteries out of the engine room etc..

Flooded batteries are such a value that abusing them does not cost you much and you can always add water if by chance you continued charging at 14.4V to 14.6V in a 130F engine bay. The batts are still damaged from this, and the life shortened, but they are cheap enough, and you can top them up with water, that designing a system around them is not worth the expense.

Incorrect charging & incomplete charging is but one part of the reason so many boaters complain of short life from typical AGM batteries. Nearly every AGM battery has different charge requirements so a so-called "smart" charges with three "dip-switch" settings is often a huge fail for many AGM or GEL batteries.

My rule of thumb with charge equipment for AGM or GEL is that unless I can fully custom manipulate/program charge voltages, absorption time etc. and it offers an on-battery temp sensor, it really has no place charging AGM or GEL batteries and the owner might as well stick with good old flooded batteries..

Buying AGM or GEL batteries and tossing them into a stock charging system is like buying a Ferrari then running a set of antique bias ply tires on it. You're simply not going to realize the performance you expect or paid for out of the batteries. Kind of like feeding a new common rail diesel through an 80 micron filter with dirty fuel... Might work for a short time but eventually it's going to cost you $$$.

Most AGM makers simply want to sell you lead so they could care less that you are improperly charging their batteries. Other than Lifeline and a few others most make you dig deep for proper charging protocols.

For example not a single one of my customers who has installed Odyssey TPPL AGM batteries, without consulting with me, knew or understood that Odyssey stipulates a minimum charge current of .4C (40% of Ah capacity) & an absorption voltage of 14.7V for "optimal cycle life". I have seen these batteries murdered in 1 year by stock Hitachi alternators feeding them .12C and barely ever breaking 14V. I have other Odyssey AGM's that I have installed as a system still performing well at 8+ years.

 

[twistedtree]

But these carbon batteries aren't any better than Lithiums are they?

Do they recharge quicker? - No
Do they last longer - probably not, maybe about the same
Can they take deeper DOD than Lithium? - No
Are they lighter weight than Lithium? - No
Are they cheaper than Lithium? - probably about the same

So where is the advantage? It's easy to compare with flooded wet cells, yes they're much better. But so are Lithiums - and they are proven technology, coming down in price as their use increases in automotive applications and Mr Musks new Gigafactory comes online. I think you're all looking in the wrong direction...

I think the big advantage is that the CF batteries can work with existing charging and inverting systems, i.e. they are more or less drop in replacements. That makes market adoption MUCH easier and faster.

LiFePO batteries require a bunch of battery management apparatus around them if used with existing chargers and inverters, and ideally chargers that a designed specifically for LiFePO. These battery management systems (BMS) are coming along, but it's still way too immature and home brew for any large scale adoption. So market penetration will be much slower.

The Musk battery pack has gotten lots of attention, but integrating it into a boat would be a major undertaking and require all new inverters and charging systems. Why? Because it's something like a 100-200V battery pack, so you need charging devices and inverters that operate at those voltages. They exist for industrial applications, but are very expensive and not installed in anyone's boat except maybe something way bigger than any of us own.

None of this means these new technologies can't make it to the main stream. It just means that it will take time, and the benefits will have to justify the effort that's required for the infrastructure change over. CF batteries appear to have one distinct advantage, but are easy to deploy. LiFePO has numerous advantages, but is distinctly harder to deploy.

 

[CMS]

But these carbon batteries aren't any better than Lithiums are they?

Do they recharge quicker? - No
Do they last longer - probably not, maybe about the same
Can they take deeper DOD than Lithium? - No
Are they lighter weight than Lithium? - No
Are they cheaper than Lithium? - probably about the same

So where is the advantage? It's easy to compare with flooded wet cells, yes they're much better. But so are Lithiums - and they are proven technology, coming down in price as their use increases in automotive applications and Mr Musks new Gigafactory comes online. I think you're all looking in the wrong direction...

Firefly's I consider a stepping stone or bridge step between traditional lead and LFP. No they can't compete with LFP in many areas because they are still lead acid batteries.

An installed LFP (LiFePO4) system, done correctly & safely, is significantly more costly than a Firefly bank and they are considerably more finicky than lead for poor charging practices. Just ask the guy who's 10K LFP battery is sitting on my bench right now ready to be recycled due to improper charging (charged at 3.65VPC per the manufacturers suggestions and destroyed).......

Yes AGM & GEL should be installed as a system but this system is still considerably less complex and far less costly than a safely & correctly installed LFP installation with BMS, charge & loads bus etc. etc..

I run LFP on my own vessel but I am also the first to admit this technology is not prime-time ready unless you have deep pockets and can pay for a quality factory engineered system and then also pay for all the correct equipment that is going to be compatible with it. The vast majority of lead acid charge source equipment out there is simply not compatible with LFP and they stuff that can be tweaked and made (quasi) compatible is expensive....

 

[Trundlebug]

Lots of work going into magnesium batteries, and have had some breakthroughs, just not yet there. I think it will happen. Lots more magnesium around than Lithium.
Magnesium To Replace Lithium-ion Batteries Soon | OilPrice.com

When and if they get it, Lithium demand will plummet, but consumers of DC power will be very happy.

Researchers at Toyota have discovered a new electrode for magnesium batteries
Breakthrough in Magnesium Batteries - ECS

Toyota is of course an innovative car company, so their goal is to use magnesium not lithium batteries. Lithium supplies are limited.

Toyota scientists make breakthrough on safer, smarter batteries

I take the points above regarding charging system compatibility, and from that I can see why carbon foam batts are of interest.

Two points though, Magnesium batteries could still be 20 years away - as stated in one of the links in your post.

Also, Lithium supplies aren't limited at all. There's lots of it in sea water. Therefore salt flats are an ideal source, where sea water salts have been concentrated. Production facilities may be limited currently, but Lithium certainly isn't in short supply.

 

[BandB]

I think one thing to keep in mind when talking battery technologies is how slow the changes occur. How little has really changed in the last 50 years in terms of basic automobile batteries. We find lead, build batteries, salvage old batteries, reclaim the lead through smelters, and start it all over again. That is all in spite of huge amounts spent on research and development. Therefore, when there's a slightly better mouse trap it's worth following, whether GEL or AGM or Carbon Foam. However, if one is looking for something revolutionary rather than evolutionary, battery technology is not the place they are likely to find it.

 

[TDunn]

Actually there is about 0.18 parts per million by weight lithium in seawater. If you evaporate 1 million gallons of seawater you will get about 1.4 pounds of lithium assuming you can effectively separate it from the other salts.

 

[Daveo]

Need to buy something!

Is this a dead thread? Hope not. Need to buy new batteries on my new boat. Have a weird mix. House bank totally fried comprised of a mix of types and sizes, 6 4D lead acid 1 4D AGM and 1 8D AGM. 8D AGM was once the main engine start battery and the 4D AGM is just loose in the engine room and blocking access to various things so I want it out. I want to revert to having a dedicated engine start battery so that leaves just the 6 4Ds for the house bank. But wait, those 6 4 Ds are split into three isolatable pairs and 4 of them are in 8D sized boxes. I'm told that mixing 4 8Ds and 2 4Ds would be a no no so, if that's true, seems like my best choices are, 1; 6 new AGM 4Ds, 2; 6 new Oasis G31 fireflys, I guess that should be fireflies?, or 3; mix 4 8D and 2 6D commodity lead acid batteries knowing it isn't a great install but they are cheap. Chargers are old, a generator or shore power supplies Trace inverter/charger, a 240 volt 50 Hertz Charles shore power euro-charger, and a 130 amp alternator on main engine. Two chargers have AGM settings but may not be customizable enough for the carbon foam batts. I am embarrassed to admit I have no idea how the current and voltage from the main engine alternator to the batteries is regulated. Anticipate that boat will be away from shore power and at anchor or mooring for extended periods of time. I won't want to be running generator enough to top up batteries and do not expect to be running main enough daily, or even weekly, to get batteries from 80% SOC to 100%. That argues for greater bank capacity but also suggests that Firefly may be more forgiving of abuse. Given all I have read I think same sized AGMs might be worst choice for me. What do you think? And thanks in advance for wading through all the details. dave