The Offshore Voyaging Reference Site

Battery Replacement—Resisting The Seduction of Perfection

We recently replaced, and increased the capacity of, our house battery bank on Morgan’s Cloud. To add to the fun and games, our venerable Link 2000 battery monitor had just bit the big one after 23 years of faithful service.

While we were at it, it seemed like a good time to go through our entire battery system and upgrade it to the latest ABYC standards. For example, 23 years ago when I last went through this exercise, I was considered an early innovator (and not a little anal retentive) for fusing the batteries. But our old fuses and their mounts did not meet present standards, so it seemed like I might as well fix that too.

And, while I suspect that our battery box and the lid that kept the batteries in place in the event of a knock down were more robust than most, I was never entirely happy with the set up, so we decided to rebuild the whole area, including adding some aluminum extrusions to distribute loads to the hull ribs (aluminum boat).

Wait, there was more. If we were going to upgrade our battery size, it only made sense to add a bigger charger so we could charge the new bank with our generator in the same time as the old bank and load the generator more as well.

And then what about renewables? Seemed like it might be time to look at adding some solar panels…but what kind? And which controller/regulator to go with them? (In many ways the latter decision is more important than the former.)

Should Be Easy Enough…

Given my training as an electronics technician and my experience with boat electrical systems going back some 40 years, including three complete re-wiring projects, I thought all of this would be relatively simple to specify and design.

…Or Not

Not a bit of it. I spent days measuring, researching, and sweating over a hot computer to come up with a bill of materials.

“What took you so long, John?”, I can hear you ask. The answer? The seduction of complication. I spent over half that time “researching” the options—a euphemism for surfing the internet looking at cool technology:

I couldn’t believe how complex this stuff has become in the two decades since I last went through this process.

On and on I went…round and round…as the summer slipped away…while I got exactly nothing useful done. I was in the grips of analysis paralysis. And worse still, I had been seduced by complication and the urge to build a system that was as good as it could possibly be.

Cold Reality Shower

Finally, I sat myself down for a good talking-to that went like this:

John, my boy,

  • You are wan…wait, that will never get past my editor…how about playing with…no, that won’t fly either…but you know what I mean.
  • You have voyaged over 100,000 miles in this boat over 23 years with no significant electrical failures—there has always been electricity when we needed it—with the current relatively simple system.
  • You’re as bad as those marine electronics hobbyists that you rant about.
  • You are 65 years old and time is slipping by, do you want the greatest system in the world, or do you want to get back out sailing?

Back to Basics

So, after that self-inflicted battering, I decided that I would:

  • Install the same technology batteries. If it’s not broken, don’t fix it.
  • Install a non-networking battery management system that works just like our old Link 2000.
  • Defer worrying about solar to…maybe next year…maybe never. (Given our abhorrence of deck clutter, the contribution from solar we can properly mount will be a small percentage of our quite large electrical usage.)
  • Stick with the chargers we have, at least for the moment.
  • Concentrate on simple elegance and meeting ABYC standards in the wiring.
  • Make damned sure that the batteries will stay put in a knockdown.

In summary, I decided to duplicate the system that has served us so well for more than two decades but add a few important incremental upgrades. Or, to put it another way, focus my energies on the important stuff like making sure the batteries stay put and nothing bursts into flame, rather than getting distracted by cool features that will contribute nothing to safe and comfortable voyaging.

And, most important of all, I would get on with it!

Close Call

The point being that I, who have repeatedly ranted against unnecessary complication, nearly got seduced by the idea of building the best system, when in reality, we already had a system that worked pretty much flawlessly. How stupid is that?

Simplicity Rules

This whole exercise once again reminded me that trying to make gear on our boats perfect and insanely cool is probably the biggest obstacle to actually getting out there voyaging.

If I had given in to the seduction of complication: the fancy ads, the forum “wisdom” that says we should all have super cool renewable energy systems, lithium batteries, and on it goes…I would be a septuagenarian before we got sailing again…a broke septuagenarian.

Defining Simplicity

And, further, I think that each of us needs to define simplicity based on our own skills and needs.

For example, Phyllis and I have made decisions like having a big freezer and a relatively big boat that requires a large autopilot—part of optimizing for cruising in remote places. And that in turn requires a certain amount of complication, our generator being the most notable example. This works fine for us, albeit at a cost in money and time, because of my skills and training.

What About You?

But the complexity trap is even more dangerous for the non-technical. So if that describes you—nothing wrong with that, we are all different and I’m sure you have skills I haven’t got—at least give some consideration to going voyaging with:

  • No autopilot (use a vane gear).
  • No large fridge.
  • No freezer of significant size.

Which in turn will let you get away with:

  • A small, simple, and cheap liquid-filled lead acid battery bank.
  • A couple of properly mounted solar panels.
  • A simple, easy-to-understand battery monitoring system.

And that in turn will let you get out there sailing many months ahead of the owner who elects to go complicated, and with way more money in the cruising kitty.

And, perhaps most important of all, you will enjoy sailing your boat and enjoying the places you visit way more than if you gave in to the seduction of complexity and the unrealistic goal of perfection. A course that would inevitably condemn you to a cruise blighted by an unreliable electrical system that you are not qualified, by training, or the desire to acquire the skills, to fix.

And let me make clear that I, even though I’m a techie, will not think one jot the less of you for taking the simple way. In fact, I will admire your self-awareness and willingness not to be bum-rushed by the crowd into a way that is not yours.

Further Reading

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Steve Hodges

Perfection is the enemy of good enough! Thanks for presenting a clear summary of the decision process you used.

Geir ove

Well…. i have full control on my boat, el, solar power batt status, +++ on my phone, and mac, ipad. Victron CCGX. show it al. i like it. my boat has been for 2 weeks on the hook down in France while i jave been home, freezer, fridge , radio Tracker has been on, al easy power by solar. we 570 watt, on the back, they even gives you power in just daylight, fog,
so and al system is updated from Victron as they have made improvements, (just like Tesla do) i like it..

Marc Dacey

I spent yesterday crimping (fused) 4/0 ga. leads from the charger to the bank. Even simple isn’t simple, but I have “robust” to fall back on.

And holes to drill afore I rest!


The S & S 112 that I was PM on back in the dark ages has a custom designed vessel information systems computer that continually monitors up to 50 functions. The owner could sit in his New York office and determine whether the skipper was in his berth or on watch at any moment— while the boat was in Antarctica. And during its entire history it has accumulated about the same number of sea miles as Morgan’s Cloud has in a typical year. And even then the owner was in his office making money rather than on board.

Boats are to use.– Anything else and they are just toys to waste money on!
There is probably a significant statistical correlation between the complexity of the electrical and electronic navigational systems and how little use the yacht receives!


The choice isn’t only what’s best now, but also what technologies we commit to and which one should be leapfrogged.

In my case earlier this year I went with a cheap replacement of the dead lead-acid batteries on our already-well-loved-but-new-to-us boat and to replace the chargers dating back to 1983. This should be good enough for the next 5 years and by then, our usage patterns will have settled enough that we can make by then an informed decision based on real data. And perhaps there will be some new wonder-batteries will have proven their mettle to.


Currently we have 8 golf cart batteries that are getting old and are considering the carbon foam batteries. Your thoughts on these batteries would be appreciated.


John, I for one would be very interested in hearing your thoughts on the carbon foam batteries. Ken

Westbrook Murphy

Your posting reminded me of a favorite from a few years ago about the most dangerous words in boating: “While I’m there.”

Patrick Genovese

Very interested in your thoughts on Carbon Foam batteries.

Eric Klem

Hi John,

I think you made a wise choice to stick with what you had. Once you have a well designed and executed electrical system, it should not take much work to keep maintained over a long period of time other than replacing a few wear items like batteries. Once you have committed to a specific battery technology, the amount of work and expense to change is a lot and of very limited benefit provided that your current system works.

I see this tradeoff of getting mixed up between user requirements and specifications. Your user requirements are that you have a number of pieces of gear that you need to provide power to and you don’t want to break the bank while doing it. Adding all sorts of fancy gear would increase the impressiveness of your specifications but if you actually tried to trace it back to your user requirements, you would find that none of that stuff actually improved the true user requirements and in fact it would hurt your budgetary and reliability requirements.

We have what I consider to be one of the simplest electrical systems that meets the normal user requirements of most cruisers that don’t have enormous starting loads or anything weird like that. The system uses 2 banks, a “house” bank which is really an everything bank and an emergency start battery selected via a battery switch. Literally everything including the engine starter except the bilge pump and solar is on this battery switch which is always set to the house bank making all monitoring, alternator wires, etc very simple. To keep the emergency start battery charged, we use an echocharger but any of the similar products would work. For us, this very simple system works well and has excellent reliability. I have yet to find a situation where a more complicated system would have actually improved my user experience. The promise of higher battery capacity with a newer battery technology is tempting but in the end we have enough capacity in our bank for our needs and we would have to change too much stuff.

One of the interesting things that I notice for people who change back to coastal cruising from long distance liveaboard type cruising is that they maintain their boat at the same complexity level as before. I often notice that due to this, these people spend more time working on their boats than using them. For some of these people who have really gone to coastal type sailing, maintaining stuff like fancy liferafts, HF radios, weather receiving gear, etc can really become a drain.

When deciding whether to make a modification, I find it helpful to compare the projected time the modification will take to how much time it will save me in the end. For example, the solar was easy to justify as it took me about 1 hour to source parts, 2 hours of fab time to make the mounts and 2 hours of install time and I have gotten hours of peace and quiet at anchor plus longer battery life.


Marc Dacey

Eric, that is very close to the system I am currently setting up. The start battery is supplied from an echo charger; all other charge sources go to the (quite large) house battery. A switch allows the start battery to be a temporary house battery if needed.

David Howes

Thank you for this piece. I think I have read everything you have written on AAC, and have learned an awful lot. This note is a validation of your suggestions from a person with no technical skills and who has adopted much that you have suggested.
When upgrading Margalo, a 1983 37 foot Pacific Seacraft, over the past couple of years, I went for a fridge with no freezer, Solbian solar panels, a 120 amp alternator and regulator that came with our new Yanmar engine, a Victron monitor, and a Wind Pilot Pacific vane.
We added a Raymarine autopilot for use when under power, an isolator for our charging system, and 5 Firefly carbon foam batteries (the data on their tolerance to low-charge states and durability appears solid).
Time will tell. But we’re out here (on the seawall at Horta as I write). Some stuff has gone wrong, lots has gone right, and it has all been understandable and fixable…….so
And we are having great fun!
Thank you……

Francis Livingston

Hi John – I would love to hear your thoughts on other battery technologies

Robert Muir

Excellent decision process John!

I just upgraded mine in a recent refit. For me, Victron and Firefly batteries was the way to go. Nigel’s experiences with carbon foam threw me over. So far I haven’t really stressed them, since we’re mostly motoring through the fjords in PNW BC and AK, but I like having the capability of being able to take them down to 25% before running the alternator to get them back to 80%. Not trying to convince you (at $425+US each, and probably currently production constrained, they’re a tough choice), just giving a data point.

I chucked the old manual 1-2-all-none switches and went with Blueseas remote switches and remote ACRs between the banks. LOVE them!!!

Brian Lockett

Great article. As usual, much good info. But one very important number – 65. Your age. Don’t get too bogged down. Flooded cells are great and affordable. Last at least five years. Go sailing! Also, we pray our Link 2000 will keep going.

Eric Klem

Hi John,

Not to create controversy but I am not sure the freezing concern is entirely valid. During cold weather, the self discharge rate of lead acids becomes extremely low. We leave our solar hooked up until mid November when we put our cover on and then hook it back up in early April each year so the batteries are not on a charger for several months. When we take the cover off in the spring, they have always been fully charged. I remember reading something that Rod Collins did where he measured voltage throughout the winter and found that the battery stayed charged. If I remember right, his recommendation was to not worry about it as it is dangerous to either leave a charger on all winter or try to get batteries off the boat every year. If we were storing in some place warm, then we would definitely be worried about self discharge from a sulfation point of view.


Marc Dacey

Well, having just spent considerable time and effort to get them in, my flooded will stay most definitely aboard if they’re not busted in a Toronto winter. I can keep a charge on in a yard, but when my other boat has been in an unpowered yard, I’ve brought down a Honda 2000 to supply enough juice to run that smaller vessel’s 10 amp charger, which has sufficed assuming I’ve put them away topped up and happy. This is no slag on AGMs, save that I don’t mind the “service” liquid acid batteries require (I inevitably do other jobs aboard when I “visit”) and I do like the money left in my pocket.

That said, one of the greatest strengths of AGM is their impressive ability not to dribble out amperage over the months. They are clearly a great choice for a mooring or a minimally equipped (no solar) boat. To each his own.



Thanks for this article. I saved 200 USD as I changed my desicion to upgrade my old boat PC whith a SSD drive.

I had convinced myself that I would save electricity and startup time whith a SSD.

Yep I would have saved 3 minutes/day and less than 1Ah:-)

Off course I had also the safety issue back in my head. A SSD would be much “safer” as it less sensitive for vibrations.

In my 25 years of computing I have had two HD crashes. One was a tradidional HD and the other one a SSD!

My desire to get a SSD for the Boat PC was just “Seduction of perfection”.

We did have flooded batteries for many years and never had any problems when we left them inside the boat over the winter (not connected). Boat was always stored outside and it could be 2-3 month whith temp. under freezing. Lower temp. is actually an advantage as selfdischarge is lower.

I was very happy with flooded batteries!

I went for Lifeline AGM when we started cruising in warmer climates. Leaving flooded batteries for 6 month in hot climates, would not work, due to the higher selfdischarge. Actually the selfdischarge issue was the only reason why I decided to pay twice as much for the Ah.

Leaving the boat on a battery charger, solar panel for six month is not alternative for me. To many things can go wrong.

When it was time for my second set of AGM I was considering Lithium. After reaearch I came to the conclusion that Lithium is a better battery, but not the best economical or practical solution on
my boat.



Chuck B

At one place I worked we had a saying: “Done is better than better.” 🙂


Robbie Collins

There is actually a question below.

As I write, our batteries are wheezing and sputtering as their last bit of capacity gets smaller and smaller. I am reminded that if the capacity falls by one-half each day the decline could, theoretically, go on forever. Oh Joy. Oh Bliss. Ever hopeful I read this most recent article in the vain hope you would say, at last, at last, at long last, Yes, buy lithium ion batteries tonight. But noooo.

So I’m turning my back on updated technology and replacing the bank with exactly what I had before: about 900Ah of AGM batteries powering a full time cruising boat currently basting in the Balinese sun. I not complaining about being in Bali, you understand. No. I am complaining about trying to source batteries in the greater Indonesia, Malaysia, Singapore, Thailand or Vietnam megaplex. And not just any battery, mind you. No, I need a special battery. I need a battery that is slim because the builder of our boat reviewed the drawings and discovered that 99% of the battery configurations on the Planet Earth would not fit unless they were, well … slim. Try getting a slim battery in Indonesia. At the end of the day the only battery which might reasonably reach me in Malaysia in time for Christmas is the Mastervolt AGM SL-185 12 V. It comes from the Netherlands. It speaks Dutch. It fits. But…..

You’ve said, and I believe, that a battery which cannot be equalized doesn’t belong on a cruising sailboat. We are frequently 2 months away from shore power … 3 months at this writing, and although we try to have at least one charge to 100% per month when off the grid, that goal is, from time to time, more aspirational than real. Mastervolt’s literature seems threatenly and suspiciously silent on the issue. So, having snatched the lithium ion dream candy out of my hands, I turn to you now begging that you know for a fact, or you’re pretty sure, or it probably maybe wouldn’t be a necessarily baaad idea to equalize Mastervolt AGMs.

Cheers, Robbie

Marc Dacey

I find it intriguing that “We, who have the same sort of space issues” comes up in terms of a 50 foot plus boat and battery stowage. Perhaps the future of boat design will acknowledge that big banks aboard in accessible places is, ultimately, an important element of the modern cruising sailor’s wish list. I say that already knowing why so many older boats do not have space for the preferred more capacious battery banks. In the ’80s and ’90s, there just weren’t as many loads as is now the case.


Hi John,

I believe you had previously advertised to comment on the Carbon Foam Firefly Oasis! I was since eagerly looking at all your following monthly reports with the hope to get your FF battery point of view until I ran over this tread.

I have been working intensively to firstly understand how all battery types are properly recharged and secondly on the power required to properly recharge them. Consequently, I intend to have two battery banks: one for carrying the load while the other is being charged OCV. No start battery is planned in my electrical system. Will use the alternator to recharge one bank and the 4200W generator with AC sole battery chargers dedicated to each bank. Include in the electric system are a stand alone inverter and battery management monitors.

So far, I plan to install 2 x 6V Flood from Rolls (550Ah) in one bank which will be connected to the alternator. Their location in the boat is easily accessible for maintenance and properly ventilated for carrying an equalization. The second bank would be made of 4 x 12V Firefly Oasis in parallel. Their location will be hardly reachable and difficult to ventilate: therefore the FF being the right battery as you know they do not require equalization for numerous PSoC cycles, just a restoration charge at about each 14th cycle.

A. Yes John, I lots of hope to hear your comments on this famous carbon foam techno; and

B. Would you know or someone else indicating me a fabricant which markets a stand alone 120VAC charger(s) pushing a 12VDC output of 180A+ for the bulk stage (as each battery necessitates >45A per battery) and having independent voltage sensor and programmable T° compensation?

Looking forward!



Hans Karreman

Hi John
Hope your well.
First off, I’ve been a member for several years now and thoroughly enjoy reading all your brilliant advice/tips etc.
As for this topic, I’m failing badly as I’m in the process of upgrading (ie; making my hydraulic system even more difficult) which brings me to the question.
While doing this and many other refit projects, I noticed that I have some corrosion on two battery terminals.
My setup is 6xVictron 165AGM’s in series/parallel in a 24v house bank.
All batteries were bought at the same time/vendor from the same batch. All cables were replaced and the system was charged by a Masstervolt 50A shore power charger (has been upgraded to a 100A Whisper Power charger.
The batteries are 7 years old now, however, on two separate batteries (and separate series connected batteries) on one terminal (the +/- connection end), there is corrosion.
I can’t explain it and was wondering if you have any ideas.
They are all located in the same location under floor in the cabin, never see any moisture etc.
I know this isn’t the topic for this comment but couldn’t find a closer matching topic.


Hans Karreman

Thanks for the reply John.
When replacing all the batteries/cables, I did pay special attention to cable lengths so that they are all equal.
I’ll check the voltage next time I’m at the boat.