What Battery Type Should You Buy?

Battery Shopping

This article has now been replaced by two new chapters, one on lithium and the other on lead acid batteries in our Electrical Systems Online Book.

What battery type should you buy? Liquid filled, Gel, or AGM?

The first thing to understand is that all three types are lead-acid batteries and use the same electrolyte and are subject to the same vulnerability to failure from sulfating. So there is no best type. Rather the best battery for you depends on your usage profile. Let’s look at the three types and their different advantages and disadvantages in cruising yacht use.

Liquid Filled

  • Lowest cost of the three types. (I’m assuming high quality deep cycle batteries for all types.)
  • Most robust and tolerant of charging mistakes, mainly because electrolyte that has been boiled off by overcharging can be topped up.
  • State of charge can be determined by measuring the specific gravity of each cell with a hydrometer.
  • Can be equalized to remove sulfation.
  • Must be easily accessible for checking and topping up with distilled water at regular intervals. Although this can be reduced with the use of recombining caps.
  • Must be secured upright so they don’t leak.
  • Must be charged regularly, even when the boat is unattended and unused, otherwise they will self-discharge and eventually sulfate and fail. In addition, a discharged battery will freeze, whereas a fully charged one will not (except at extreme temperatures not normally encountered where yachts are stored).

Common to Gel and AGM (Sealed Batteries)

  • Can generally be installed in any orientation, but check manufacturer’s recommendations.
  • Access for regular maintenance is not required; however, all batteries should be well ventilated, so don’t bury them in a sealed locker—kaboom can ruin your entire day.
  • Have a very low self discharge rate and therefore can be left fully charged for long periods (a year or more) without charging and without fear of freezing.


  • Generally cheaper than AGM.
  • While I have no solid engineering based proof of this, it does seem, based on our own experience and that of many other voyagers (received through the comments to this site), that Gel cells are less subject to sulfating from not being fully charged after each use than AGMs.
  • Generally higher cost than liquid filled, although this can vary depending on the quality of the two types being compared.
  • Are the most vulnerable to overcharging of the three types.
  • I have never seen a Gel cell battery that can be equalized, so once they sulfate, and all batteries do eventually, particularly with the usage profile of the typical cruising boat, they can’t be resuscitated and must be replaced.


  • Have a significantly higher acceptance current (amperage) than the other two types. This means that they can be charged in less time, particularly up to about 85% of full charge. And, by the way, according to bench testing at LifeLine Battery, AGMs, or at least their AGMs, actually last longer if charged fast, as long as the acceptance voltage is not exceeded.
  • Have a higher capacity for a given size than the other two types (10-25%).
  • AGM batteries from some manufacturers can be equalized.
  • By far the most expensive of the three types.
  • Are the most vulnerable of the three types to premature failure from sulfation if not fully charged after each discharge, which is impractical on most voyaging boats that don’t see shore power for months at a time. This problem can be largely overcome by following the protocols in this Online Book and/or by having substantial solar charging capacity. Again, I have no engineering proof to backup this assertion, and I suspect it will raise howls from AGM battery manufacturers, but our own experience, and that of many other voyagers, is just too compelling to ignore.
  • Many AGM battery manufacturers specifically forbid equalizing. These batteries should be avoided by pretty much all cruisers because this restriction, coupled with the point above, can result in lifecycle costs of as much as US$5.00 per discharge! This I know from bitter experience.

OK, What’s Best, Dammit?

That was fun…confusing, too. “But what battery is best for a cruiser?” I hear you ask. Well, it depends. Don’t you hate that answer? Why is nothing ever simple in cruising? Let’s have a go at simplifying it as best we can.

The Budget Option

If you have easy access to your battery area, a tight budget, and don’t need to leave your boat unattended for long periods, or can arrange for someone else to charge the batteries once a month if you do, then liquid filled is the way to go. We have even heard of cruisers that have had good experience using golf cart batteries that can be bought for much less than their marine equivalents.

The Middle Option

[I changed this section on Gels on 17 Jan as a result of Dick’s comment (see below) and a re-read of other comments from Gel users.]

I’m going to go out on a limb here, and probably get beaten all over the head and chest in the comments, but I generally don’t recommend Gel cells for most cruisers, for one simple reason: I have never seen any that can be equalized and, therefore, when they do sulfate as a result of not fully charging after each discharge, there is no way to bring them back to life.

Having said that, we used Gels for some years with great success when our usage was much lower than it is today. You may want to consider Gels to get the sealed battery advantages at a lower cost than AGMs as long as you can fully charge them to 100% regularly. (By the way, there is only one way to know that your batteries are fully charged.)  Or, if you simply don’t want the bother and aggravation of regular equalization, then gels are likely a better and longer lived option than AGMs.

The Expensive Option

If, like us, you need to be able to leave your boat unattended without worrying about getting someone to charge the batteries regularly, and particularly if you don’t have as much room as you would like, or really need, for batteries (again like us), AGMs are the way to go. But make sure that the ones you buy can be equalized, and that you follow the protocols in this Online Book to care for them, or there will be tears—trust me, this I know.


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Nick Kats

Where’s the sidebar?
Hemidemisemicomputerliterate&allfrustrated.. Thanks!

Nick Kats

Got it, thanks John!

Erik de Jong

Hi John,

Great piece.
The only addition I’d like to make as a disadvantage of liquid filled batteries, is that they should be placed in a sealed and ventilated battery box in order to avoid poisoned gas in the living quarters during charging. This is also a recommendation for all sealed batteries, but much less critical.

Jean Jutras


I am an “early adaptor” and like new technologies. Many new products and technologies, nowadays, tend to be reliable (but often more expensive). Next year, I am planning to replace my AGM batteries by the MASTERVOLT Lithium Ion ultra. These batteries will equip all the yachts of the Volvo Ocean Race, not only for the 2014-15 race but also for the 2017-18 race.

Many manufacturers are now offering this type of batteries but is the quality and reliability the same? It will be interesting to read more about it in the next post and if someone has tried to use it, their comments will be more than welcome.

(Sailing a Cabo Rico 42)

Dick Stevenson

Dear John,
I thought I would share my experience with gel cell batteries as it differs some from the conclusions you reached and therefore affects the recommendations you make.
I have been using gels for 20+ years: at first Sonnenshein (sp?) and for the last 15 years East Penn batteries. From the beginning I have used Dave Smead’s (Ample Power) charging protocols which I believe to be a bit more aggressive than generally recommended. For much of my 12 live-aboard years we have lived off the grid at anchor so we could and did go months charging at 50% and bring the bank up to 80-85%. Being in the trades during this time, there would be rare long powering that would bring the bank to full charge (possibly about once every 6 weeks or so). We have a big freezer so this charging regimen (DC genset) would be at least once a day and often twice in hot water and high temps. The gels tolerated this extremely well. We would get 6-7 years out of our battery bank.
I continued with gels as they tolerated this use very well. I agree with your observation that gels are less subject to sulphating from not being fully charged than AGMs, although my research in the AGM realm is anecdotal and casual. When I looked into AGMs I felt their need to be fully charged on a regular basis was not possible in the live-aboard life I was then encountering. Now that I am in Europe, where we are so often in marinas, AGMs might make more sense.
As to not recommending gels because they are unable to be equalized: this to me does not seem fair as they are not made to be equalized. I know by this you are implying a shorter life because of sulfation that is unable to be reversed, but this has not happened in my experience with gels. I get good longevity in my estimation. And certainly I have never experienced the sulfation happening in weeks or months that you warn of in such a foreboding manner.
I am now moving into areas where I have some experience, but not a lot. I believe the equivalent to equalization for gels is a process called conditioning whereby the battery bank is fully depleted (down to 10.5v over a 20 hour period) in a graduated fashion and then brought back to full charge. I used this conditioning technique regularly before living aboard full time and felt it made a difference, especially when the battery bank was starting to show itself wearing out. Since living aboard full time, I have let this slip away as the whole process takes so long and is hard to manage the consistent amperage draw that conditioning requires. I have not felt the longevity of the battery bank has been compromised by not conditioning, perhaps full time use is in some ways kinder?
You said you were going out on a limb and I would wish, in the kindest possible way, to cut it off by saying that your statement: “ therefore, just a few months, or even weeks, of not fully charging after each discharge can result in their demise from sulfation with no way to get them back” does not meet with my experience with gels I have been using.
So, in summary, I install the battery bank and basically forget about the batteries for 6-7 years (or more). I replace before they start to die as that is how I run my boat. I do not have to worry about equalizing nor do I any longer condition the bank, although I keep that as an option if deemed necessary. Being an all DC boat with a large freezer, we have a higher than average daily amperage draw, so I consider the battery bank to be used hard. My casual research into AGMs lead me to believe them to be fussier and a bit more fragile so I have stuck with gels and continue to see them as a great option for those who demand a lot from their battery bank and live off the grid for long periods.
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Dear John,
I will look forward to the re-write.
AGMs may have a longer life if cared for in the ways you describe, but I feel I get about the same or better life than those I know with AGMs. That said, mine is a casual comparing of notes over the transom type of data collection and I believe that none I know comes close to your maintenance diligence nor do I know anyone who equalizes their AGMs. At this point, I know I will still opt for the maintenance simplicity of gels and take the chance that they may not last quite as long.
I am curious about whether any of the readers know/use the conditioning technique I described with their gels or what the current thinking is in this area.
My best, Dick

Eric Klem

Sorry John, this isn’t something that I have ever worked on or studied and I don’t have any insight. Hopefully Matt or someone else does.



The largest gel cells I’ve worked with are little 5-pound general purpose things. I don’t have experience with large gel cell banks.
From what I do know about their chemistry, I would suspect that deep discharging of a gel cell would turn the surfaces of both plates into lead (II) sulphate, just as with any other lead-acid cell. Perhaps the idea is that, when the plates transform back to lead and lead oxide on recharging, the surface texture has changed to expose more fresh material…. but that would seem to imply that we’re intentionally damaging the plates to hide the sulphation. And we can’t overcharge (equalize) to actually remove the lead sulphate that will inevitably build up.
Not sure if that’s entirely right, I’m open to being corrected by someone with more expertise in these things.


I think that if you know you’re going to abuse the batteries, nickel-iron ones might be a better choice than any of the lead-acid types. They’re very tolerant of being run flat, overcharged, ignored or otherwise abused, and will probably outlive the hull itself.
The trouble is that they self-discharge much faster than any lead-acid battery (if you leave the boat unattended for six months, they will probably be dead) and they cost twice as much- if you can even find them.

Dick Stevenson

John, I have always noticed that one of the selling points of AGM batteries was their high acceptance rate. That sounds wonderful on paper, and then I wondered how many boats had the capacity to charge their AGM battery bank at anywhere even close to the battery’s acceptance rate. Couple this with your recent comments that AGMs like to be charged fast and I would think that many boats would have challenges in this area.
Dick Stevenson, s/v Alchemy

Matt Boney

One point that needs clarification is that AGMs can be charged much faster than flooded wet lead acid batteries because their “charge efficiency” is much better. Wet cells may be only 70% efficient which means about 140Ah must be put in to actually raise the capacity of a battery by 100Ah. (70% of 140Ah is 100Ah)
AGMs may be up to 98% efficient so only 102 Ah needs to be put in. That’s nearly 40% less Ah needed so 40% faster charging, and it doesn’t take a large alternator to do it. Even solar panel will charge faster.


Installing a high output large-case alternator may take a fair bit of fuss, but I have yet to see a cruising boat of any kind where it isn’t worthwhile. The time and expense of periodically rebuilding a burned out small-case alternator (which is really just meant to power instruments and lights) more than cancels out the up-front cost of a good one. Add the improved lifespan of batteries that aren’t consistently under-charged, and the shorter engine running times, and a decent high-output charging system starts to make quite a lot of sense.

Dick Stevenson

John, I forgot to include the initiating reason for the above post. Given AGMs wish for quick charging and problems that occur with slower charging, what does this mean for the increasing number of vessels relying on passive charging methods which are invariably slow charging? Dick


have any of you advanced types researched the nikel iron (Edison) battery for marine purposes?

(Forgive if this is not appropriate suggestion-question. This sort of thing is beyond my pay grade, but this type of battery has always impressed me as deserving of more attention. Old technology, but solid and long-lasting, with many of them lasting for decades.)


Hello, I just joined AAC, we are in the process of buying a Krogen 42 trawler to fullfill a long-held dream of economical long-distance traveling in comfort ;-). Being new to the website, I hope this is the right place to make this inquiry, and that I am not creating a conflict of interest for the website.

Does anyone have any experience with TPPL (thin plate pure lead) technology?
Here’s an article about it: http://www.passagemaker.com/channels/new-battery-technology/
Here’s an example of one: http://www.odysseybatteries.com

John, if this is the wrong place for my comment/inquiry, please move with my apology.

Thanks, Wil


John, well, that was fun. I called Odyssey Battery and the tech who answered didn’t know what ‘equalization’ or ‘conditioning’ were. I explained them to him and he said ‘it will damage our batteries if they are taken above 15.2v while charging’. Seemed to think I was a nut of some kind. Come to think of it….. Anyhow, Lifeline AGMs will do nicely.
PS: I don’t think the anti-spam math is that onerous at all if it keeps the web-crawlers out.

Geir Ove

we did install 4 x 6V 390 amp Trojans, so thats 12V 780apm, and we got hold of Hoppecke pluggs to use one the cells, here is what they do,
The AquaGen® premium.top recombinator is fitted to the battery as an external component. This avoids any temperature rise inside the battery. The separation of the recombination process from the active components of the battery allows maximisation of freedom from maintenance, as for sealed batteries, without reducing life expectancy and with no restrictions on operation of the battery.
— And our 6 month sailing duering the summer Norway and Scotland, Our batterys did not need any refill of water.
we have 3 x 190 watt solar, and did run engines a bit due to no wind for a week in Scotland. we have 2kw inverter making coffe every morning, ++ never did get our bank down more then 78%.


These plugs works.

Marc Dacey

Thank you for this information. These devices seem similar to Hydrocaps (http://www.hydrocapcorp.com/) but seem significantly taller, which would create some issues around some potential battery locations. Does the Aquagen recombinator product do the same thing as the Hydrocap “vent”?

Thank you.

Geir Ove

Mine are not tall type, they only build about 4-5cm above the batt. if you look or zooom in on the picture you can se my type in the backgound.

Marc Dacey

Thank you, Geir, for the clarification. I see them now. Much better for most installations, I think.

Bill Wakefield

Hi John,

We were faced with replacing our house bank last summer, and benefitted from this article and ensuing comments.

I decided to use wet cells once we discovered a remote battery watering system specific to the batteries I selected. [Trojan Hydrolink]

I can water the remotely located bank of eight 6 volt batteries in about 30 seconds (including getting things out and putting them away…

I believe remote watering systems like this may negate that one con for liquid batteries.

If it is appropriate to include here, following is a link to my blog post detailing that project including product information links: http://svdenalirosenc43.blogspot.com/2014/11/new-batteries-with-built-in-watering.html

Best Regards,

-Bill Wakefield

Jeff Conrad

Hi John,

Great site, as necessity being the mother of invention, I have joined up while researching batteries due to failure of my house bank of 3 8D AGM (Deka), 198 AH each. Without retelling the long saga of how I arrived here in Sint Maarten now scrambling to restore power to my boat, I do have a couple of quick questions for you. The first deals with knowing you have arrived at full charge on you batteries. I have understood the criteria as you state multiple times in your online book, that being current dropping to about 1-2% of battery capacity while at an absorption voltage around 14.3V. As I am about to purchase new Lifeline AGMs I have been reading their technical manual where it states “The battery is fully charged when the current drops below 0.5% of the batteries rated capacity (0.5A for a 100AH battery).” Can you explain the difference in the full charge definition? This is kind of important as I will need to input this parameter into my LinkPro monitoring system in order to receive a proper indication of when I have reached full charge.
My second question is have you any information, anecdotal or hard data, related to desulfators. Here in Sint Maarten I have bought a couple of these units from a local producer and plan to use them on my new batteries. The engineer here swears they work to not only prevent sulphation but, under the right circumstances, restore capacity to a sulphated battery.
Thanks for your time and great site.

S/V SeaSparrow
Halifax, NS


My experience with de-sulphating is with truck batteries and many chargers automatically sense the need for this type of charge, usually in the 16V range for about 3 hours. I would not do this in the confined space of an engine room. When the battery has been left for too long a time and with a reading below 12V you maybe too late and be very careful if the battery was exposed to freezing temps. Protect your eyes!!


I just ran a cross a new/revisited technology. Interesting: salt water batteries. Check the the startup company Aquion. Not currently used in mobile application, less energy density that lead acid. See the white paper comparison. Could have advantages for electric propulsion (by design not conversion).

richard s (s/v lakota)

as a non-engineer yet decently experienced sailboat cruising buff i still say all this is much more art than science that often stumps so-called marine mechanics…richard s (tampa bay)



maybe I missed it in one of the chapters on batteries, but I cannot recall you talking about TPPL batteries (Thin Plate Pure Lead). They have been around for several years (10?) and they have a much higher Charge Acceptance Rate then any other lead based battery.

While more expensive then AGM or Gel batteries, they are much cheaper then Lithium Ion.

Many articles have been written about then, here is one for reference:

Any thoughts? Thanks










I hope you don’t mind my jumping in here with a detailed real life example.

I have read this thread and the entire series of battery articles with great interest.

I have recently gone through the process of trying to optimize my house battery bank on a Nordic Tug 37 (I know it’s a coastal cruiser not offshore vessel but we frequently spend weeks off & away from shore power as well as frequent trips in the dead of winter – perhaps not unlike an offshore cruiser might.)

My system consisted of:
Main House Bank: 4 x 260 Ah 6V Discover AGM “traction” batteries giving 520Ah of 12V power. (This would give me 260 Ah of usable capacity allowing for 50% discharge rates.)

Secondary House Bank: 2 x 220 Ah 6V Full River AGM’s in the stern. This remote bank connects in parallel to the main bank with 2 runs of 2/0 cable (~25 feet). These function as accessory power to the House Bank and the primary supply for the Stern Thruster. (In theory this should add another 110 Ah of usable capacity.)

Total Usable power = 370 Ah

I have a 11 KW Onan Diesel Generator able to charge a Xantrex Freedom 25 Inverter charger as well as a Xantrex TrueCharge 40+ Amp Multi-stage Charger. The Freedom 25 can charge up to 130A quite happily if the battery bank can take it.

I have also installed 2 x 280 Watts of solar panels on the Pilothouse roof charging via a Tristar MPPT controller. On bright sunny days, I get 25-35 Amps of charging from these panels but rarely completely charge the battery bank with solar alone. In the winter months we see far less help from the Solar system.

I am able to monitor usage and charging via a Victron BMV-700 Shunt.

One would think that this would be a more than adequate setup but…when out in the winter here on the BC Coast, I have a Wallas diesel heater running continuously along with a Fridge and Freezer + LED lighting & other draws etc. This gives me average ongoing power usage of 12-16 Amps or approximately 300-360 Ah per 24 hour day.

I was finding that even starting off at a full charge at 1030 in the AM we would be down to 12.1V by morning the next day. These AGM’s are not supposed to be partially recharged so generator runs have necessarily been a good 3 hours to try and get that last 10% back into the battery bank. My batteries have instructions that strictly forbid equalization making me concerned that I should not scrimp on recharging them to close to capacity.

It seems to me that if the battery bank could tolerate recharging to ~80% SOC, then one could reduce generator runs to 2 hours and on brighter days even forgo any generator usage.

I understand that the Firefly AGM’s with their Carbon Foam Structure will tolerate sustained partial states of charge without damage or sulfation. In addition, unlike the standard AGM’s, they are supposed to also be able to tolerate discharges down to 10% SOC without damage. They are also supposed to be able to accept higher charging currents than standard AGM’s maximizing the efficiency of charging .

These tempting benefits prompted me to recently swap out my main house bank AGM’s for (6) Firefly 12V 110 Ah batteries giving me ~ 660 Ah of capacity of which ~ 600 Ah should be usable; not counting the ~110 Ah from the Thruster Bank.


I have only recently completed the installation.

My first overnight usages (anchoring at the end of a few daily motor runs) have been in the range of 230 Ah & have not yet really stressed the system. (Morning voltages are running in the 12.43V range. ) My initial impression is that the batteries operate at slightly lower voltages for their given state of charge but that the discharge voltage curve is considerably flatter than that the old AGM’s.

This is all a rather round about way of saying that one might consider Carbon Foam AGM’s as an alternative to standard AGM’s. If people are interested at all in this alternative, I would be happy to report back once I have more experience using the Fireflies…


Thanks John,

I explored Lithium as an option but balked at the prospect of the need for a very different charging profile. I have several other AGM’s in the boat including an 8D AGM servicing the bow thruster & windlass as well as an 8D AGM start battery & smaller G31 AGM generator start battery. If I were to go to Lithium I would have had to swap these out as well. To adopt a new charging system and replace all the AGM’s would have been an enormous expense & hassle.

The Carbon Foam make sense. I hope they live up to the promise.

We are pretty lucky to be able cruise all year round. It’s cold at times but very beautiful. We often have anchorages to ourselves that would be jammed with boats in July.


Martin Wagstaff

Hi John, first of all what an amazing source of information. I have been a member for a while but this is my first post. I have just read everything about batteries and charging and I’m glad I did before spending a great deal of money in the wrong thing. To quickly summerise we are currently refitting our Oyster 47 to go around the world. The current batteries are alive but will need replacing before we go. Currently we have 4 x 6v batteries in series parallel for a 12v system. I will be doing a power survey shortly to work out my AmpHrs but what are your thoughts on 6v and 12v batteries? I can’t seem to find any logical reasoning to decide what is best. Martin

Martin Wagstaff

Hi John,
I look forward to reading it. I have a year before I need to take the plunge and purchase them,

Murray Fitzgerald

G’day John.
We are on our second set of AGM batteries. First set lasted 8 years & were changed out because we were sailing around Australia. As you said the trick is to keep them topped up. We have solar & an engine generator with a battery management system that swaps the charge between house & engine battery depending on need. It will take a good argument to get me away from AGM.
P.S. plenty of sun in Australia!!


Hello John. You wrote: “I have never seen a Gel cell battery that can be equalized…”. Please see https://www.hoppecke.com/en/product/grid-power-vr-l/ download “Operating Instructions”, page 40. Based on certain conditions, those OPzV (GEL) batteries have a procedure for equalizing at up to 2.4 V/cell for up to 48 hours. Best regards, Markus.

John Crossen

Not sure this is the best page for this question but this where I was directed. What is the best way to power a 100amp windlass? Currently, we’re using the 30-yr old factory-installed cables (approx 30′ long each way), but every time we use it we get a low voltage alarm (set at 10.8v) on our chartplotter. The batts are 6 T-105s, about 3 years old, the Maxwell windlass (VW2500) is about 2 yrs old, and we’ve observed no other obvious signs of low batteries. When I installed the windlass I noticed the cables were stiff, but not solid; they reminded me of welding cables, but there was no visible signs of corrosion when I attached the new ends. We’re looking at 2 options….(1)replacing the old cables with new, or (2)installing a new, separate, dedicated battery in the chain well. But if so, what size batt, and how best to recharge it. Both are about equal in cost; which would be recommended? Also, we are running the engine when the “low-voltage alarm” comes on, but typically only at idle. The alternator is a factory standard 80 amp, with internal regulation, that feeds the house bank directly. We do have a separate dedicated start battery, that is recharged via a Balmar Duo-Charge.

Rob Gill

We too replaced our original windlass about four years ago with a Maxwell (different model but same 1200 wattage). Had exactly the same low voltage alarm on our chart plotter, also even with the engine going. Our Raymarine electronics would shut themselves down if the windlass was really working (not great timing as we would lose depth, speed, rudder angle and suddenly have no chart display). If the windlass was really working, it was most likely in the poorest conditions, when we needed situational information at the helm.
Having no power issues to the windlass, we suspected the batteries as they were 6 years old and needed replacing anyway. New LiPo batteries were installed in due course, but the problem continued. We replaced the supply and return cables with heavier duty cable to the main bus bars (factory originals probably spec’d to a budget) and the issue resolved – no recurrence since. I suspect John is probably spot on (as usual).
Br. Rob

Rob Ramsey

Hi John & all. Great stuff on batteries! What do you think of the new lead-carbon batteries? Seeing that Victron now sells them (https://www.victronenergy.com/upload/documents/Datasheet-Lead-carbon-battery-EN.pdf) I would think they are mainstream now. The battery can be discharged to 100% DoD (Depth of Discharge), has a longer life than car batteries (500-1300 charge cycles according to Victron, not as long as LiFePO4) and are ideal for PSoC (partial state of charge) which is the way we use batteries as cruisers – never full, never empty, always somewhere in between. They are also called ultra batteries (invented by the Aussies) and are basically traditional lead-acid batteries with carbon on the negative plates which then act as super capacitors. For reasons not yet fully understood this also mitigates sulphating which is good for us. They are affordable, should be charged as lead-acid, can be fast charged, do not require charging to 100% regularly, require a lot less equalising and are safe. Reading about them I got quite enthusiastic – I can get 160Ah from a 160Ah battery. Worse, If I use only 60% I could have 1300+ charge cycles. And if they quit while I’m in Nowhereland I can replace them with car batteries because chargers, inverters et cetera in the boat are all standard.

Seems like they have taken care of a lot of the disadvantages of lead-acid batteries.

So, what do you think? Interesting development for cruisers?

Rob Ramsey

Hi John. Victron seems to be modest with their numbers and they cite claims by other manufacturers as being better but they haven’t been able to confirm.

On the capacitor thing: adding a layer of carbon to the negative plate makes it a super capacitor. Here in Wikipedia https://en.wikipedia.org/wiki/UltraBattery and here on how it is made here (he’s upgrading a dead car battery to an ultrabattery, not what I would want to do, but it explains a lot): https://www.youtube.com/watch?v=beIwzjfkbyM. By the way … the company behind this does research in carbon batteries and capacitors: https://workingink.co.uk

Mind you … I don’t claim to have the knowledge or expertise to say that the Victron and Firefly are hybrid supercapacitors / batteries.

Rob Ramsey

Also … just to add … the fact that the Pb-C (lead-carbon) batteries will operatie at PSoC (partial state of charge) means they don’t require regular charging to 100% SoC (state of charge), which is great for cruising boats that have trouble recharging to 100% SoC unless on shore power. So you can use the Pb-C battery anywhere between 0% and 80% SoC without damaging it. To me this seems a huge advantage.

They require far less equalising, if any. They don’t require a BMS and other LiFePO4 regimes. As I understand you charge them like a lead-acid battery.

And … as I understand it … they have lower internal resistance so can be charged faster. So if you have solar then the few hours of high electricity production are better utilised.

Also, I must apologise … I seem to have commented on an old post.