Short Battery Life on a Cruising Boat Fixed

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JHH5-12213A year and a half after we installed a new housebank on Morgan’s Cloud, and embarked on a field test of AGM batteries and the care regime that Justin Godber at LifeLine Batteries helped us develop, we tested the batteries. Here are the results..short version, it works.

Our Usage

First off, let’s put the results in perspective by talking about our usage. After installing the batteries we spent a total of six months in a marina with shorepower available and the other 12 months out cruising.

When we were in the marina, we cycled the batteries to about 20% discharge once a day (mainly powering our diesel heater) because we turn off our shorepower when we go to bed—the hum of the isolation transformer and the whirr of the charger fans is very irritating. A comparatively light use.

Once we got out cruising our batteries got a real workout with at least one 50% discharge every day and sometimes two.

So our batteries have seen some 180 20% discharges and about 400 50% discharges. They have also been abused by three 100% discharges for testing purposes (not recommended).


We ran a discharge test and were pleased to find that both batteries showed just about 90% of their original capacity left, which is a huge improvement on the life we got from the two sets that both died after about 400 50% discharge cycles.

While there is no knowing for sure, I would guess that, based on this test, we are going to get at least 1000 50% cycles and possibly as much as double that, before replacement—pretty impressive.

What Changed?

With the previous two sets of house batteries that failed prematurely, we had done all the usual things that conventional wisdom dictates, including installing a three stage alternator regulator and battery charger, and never discharging below 50%.

This time we took a much more active approach as documented in this Online Book, including reprogramming our alternator regulator from the factory defaults, equalizing our batteries once a month where possible, and manually managing our shorepower and alternator charging.


This has been an interesting and rewarding process that we have drawn the following conclusions from:

  • The standard wisdom about battery care is flawed and, on a sailboat that spends most of her time far from shorepower, will result in premature failure.
  • Most charging equipment, including the fancy three-stage stuff, that claims to automatically take care of your batteries, won’t.
  • There is a huge amount of absolute rubbish published and rumoured about battery care, and the “professionals” are often the worst offenders in this regard.
  • Most staff in boat yards are almost totally ignorant about proper battery care, but that does not stop them having opinions.
  • You don’t need a lot of highly expensive or complex gear to take care of your batteries properly.
  • If you follow our relatively simple “Eleven Steps to Better Battery Life” you will do fine.
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Matt Marsh

I’m glad to hear it’s working out for you, John. For an old and well-known technology, Pb-acid batteries are remarkably finicky. (Just wait until lithium-based cells start getting popular….)

“Most charging equipment, including the fancy three-stage stuff, that claims to automatically take care of your batteries, won’t.”

Anything that claims “install and forget” deserves lots of caution. It’s possible to automate everything, but it involves a lot of money, a lot of customization, a lot of sensors, and a lot of thick technical manuals.

“There is a huge amount of absolute rubbish published and rumoured about battery care, and the “professionals” are often the worst offenders in this regard.”

It does make it rather hard to do things right, when there are so many common ways to do things wrong….

Geir Ove

The single most important of the eleven steps is monthly equalization.
This sounds like a lot , is there not signals from the batts that will tell you when you need to do it ?
And are they the same for: Leads, AGM, Gel ?

Geir ove

Bob Tetrault

In prior discussions I described in detail the very similar experience I had with AGM’s before John got Jason involved . Although I took a slightly different approach to battery management I can report a much improved experience the past 18 mos. My Lifeline banks and two other non -Lifeline banks of 4D’s; service has mirrored that of Johns. I contribute this much improved service to the equalization schedule and procedure recommended by Jason. My take away from this experience; do not trust what you read on battery care! Not all batteries are “as advertised”. Bigger (heavier) is not a good indication of performance. It’s all about quality construction and understanding how to properly care for your batteries in your particular circumstances, beginning with adopting a relevant equalization schedule.

Gene Smith

Hmmmmmmmm I must be doing something wrong.
My batteries have averaged 8 years with nothing more than a Balmar ARS 4, Pro Mariner Fly Back and a jug of ionized water.

Tom Hildebrandt

Great information!

Regarding the equalization while cruising, I think you said you were at about once a month with shore power, but there may have been a 2 month hiatus from shore power? How long were your marina visits? How long did the equalization process take during these visits? Did you ever equalize from a generator during this period?

My real concern is that if, as you suggest, equalization is the key, how do you do this on the hook? As I see it there are two components, one.. what do you use to equalize whilst swinging on the hook, and two .. What do you do to segregate the essential systems from the high voltage necessary for the equalization process? (Perhaps you have the same problem whilst in a marina?)



Tom Hildebrandt

Right John, got that. I had just hoped you had some additional positive data and conclusions in these areas.

The bottom line is equalization demands two days with shore power per month, and constant monitoring for a minimum of 24 hours with at least some one awake, sort of like an anchor watch. If you have been out for longer than a month, say two months, you need to at least double that time. It just can not be efficiently done on the hook or whilst sailing/motoring.

For myself, a solo sailor, this seriously dampens the cost benefit reward for such a regime. While it may make sense for those with crew, for me it means an average of $50 bucks ( my average daily rate based on a weekly stay in a marina) for dockage and shore power or $600 per year. During that one day, I get no rest, and although I can do other tasks, I am completely tied to the vessel.

Currently T-105 lead acid batteries can be had for $160 a pop, about $120 if you have a core to exchange. So every year you could replace about 4 batteries, slightly better than 200 amp hours, for the cost of spending time at the marina equalizing.

I am thinking it makes sense for me to equalize whilst I am in a marina for other reasons, or hauled out, if I choose to spend my time for 24 hours monitoring, but regardless I will just need to accept that every year or so, I will need to replace a part of my battery bank.

Here is hoping you with a better mind on these topics than I can show me the folly of my thinking!!




Do you have a monitor system on the Morganscloud?

Erik Snel

Hi John,

Very interesting reading. I purchased 4 Sonnenschein GF-06-180v gell cells last year, and they were very expensive, so I would want to keep them for a long time. Their manual states a maximum charging voltage of 14,1V. There is no mention of equalisation or the effect of higher voltages once every time to return the cells to their optimum state. I am quite anxious to try this out and maybe throw away the equivalent of $1800!
Also, when moored (which is 80% of the time) I keep the batteries topped up with a small 20W solar panel. Would this have an adverse effect on the quality/lifetime of the batteries?

Kind regards,


Erik Snel

Hi John,

Thanks. I will charge them as I did before. And yes, the solar panel is equiped with a quality regulator. I am going to upgrade to 3 20W panels, but I guess that will make no difference as the total capacity of the set is around 400Ah.

Kind regards,


Svein Lamark, Norway

To me your batteri Lifeline seems low-quality. Allready 1980 UK manufactors said their AGM would last 10 years. Your equalization seems neurotic to me. On my expeditions shorepower is normal only after 60 days. I buy used AGMs, more than 10 years old, very cheap. There are hundreds of radio masts in The Arctic and they change batteries after 10 years. This batteries are cheap, but often ok. I only buy 2 volt batteries more than 5000 cycles. 12 volt batteries are not so good. With charging carefully at low volts they last for many years more and give plenty of power.
Batteries may fail and every expedition boat should be able to start main engine on compressed air or by hand. Sperre has a small hand driven compressor, its hard work, but takes no 12 volt.
Change to 2 volts and compressor and your problem is over.

Svein Lamark, Norway

Hi John,
I am sorry, I do not read much Freud. I have seen a German boat with 10 ruls how to pump the toilet, but 11 rules how to charge the battery is a record. I think your problem is that you have a big boat and small batteries. Big 2 volts last for 15-20 years, but they are big. Your ship is probably a masterpiece inside and has no room for big batteries, and you can not take the ax and make space. My sailboat is only 33 foot, but I make the space because I do not like the noice of a generator. My windmill is a plague. I now test new blue blades from Portugal. They are better.
My little sailboat has made 200 000 nmiles most of it north of the arctic circle in summertime. In summertime the wind is gone from that latitude, less wind for every 10 degree North. So engine makes 50% of the miles. That helps charging. I have also a motorboat that has made 120 000 hours. Modern motorboating is hard for batteries because people stay longer periods at anchor thanks to diesel prices. At Koster, Sweden you may now only stay 2 days at the same anchor spot. I am thinking of a generator for the motorboat.
You have good generator. Start it every day or sell it to me. I can give you some big batteries to put in the empety hole. (You must sail across.) . A wood fire helps, there is timber all over. Have you tried fuel cells? The Germans say it is very good: It makes no noice and batteries are always full. I do not know, but it could be the solution.

Svein Lamark, Norway

Hi John, very nice talking to you! I also think a 1000 AH big 2 volts would do it.
To day it is cold here and I heat the ship with wood fire oven. That is charming and uses no el.. I still wonder about the Fuel cells, look at Have you got any experience with this tecnology? I am very curiose about this new metode of producing el.
Best regards Svein and greetings to your wife and your good ship


Hi John,
I’m surprised that 2 volt industrial cells would require more space than your 12 volt based house bank. But perhaps the determining factor is the minimum size of available 2 volt batteries.

When I was involved in building a 112′ S & S motorsailor some years ago the owner asked me to evaluate battery systems and prepare a formal recommendation. (at the same time he paid MIT 50k to do the same study— but he always did like to blindside people!) Anyway, I talked to people I respected who were building factory trawlers and we came up with the recommendation of a battery system based upon flooded 2 volt cells that were also being used in a tourist submarine under construction at the same time. The deciding factors were proven longer life expectancy and more compact and efficient packaging in the areas between frames in the aluminum structure. Of course they went with the MIT design, incorporating the then new gel batteries and individual temperature sensors on the principle that newer is always better especially if it has a PHD attached —–. (see Boeing and Li battery for more on the same topic)



Thank you for posting your experience with your AGMs – I consider your Morgan’s Cloud report as so reliable I will be making my battery decisions based on it.

Focusing on your points of “regular full charging” and “monthly equalization”, I find that an onerous regime, especially since I do not have/want a diesel generator.

So I have decided on LiFePo cells as a house bank, the main attractions being:

a) Never needs to be equalized
b) Never needs to be fully charged (apparently 80% is enough)
c) Higher charge rates than lead acid (so when you charge, you can really pump it in)
d) Can routinely discharge down to 20% (as opposed to lead-acid’s 50%)
e) Can be left at rest, on its own, for 6 months, with low self-discharge
f) Half the size and weight of an equivalent lead-acid bank (friendlier than the 2volt 1000AH back strainers mentioned above).

The main downside (I currently understand; I’m no expert) is that you rely on an electronic cut-off device to ensure voltage remains between an upper and lower limit at all times. This high/low cut-off protection may not be dissimilar to keeping a Gel battery between upper and lower voltage limits, except that the voltage range is smaller, so the cut-off sensing must be more accurate.

You also have to keep an eye on inter-cell balance, but reading boat forums where LiFePos are used, it seems this can be monitored easily, and if re-balancing is required, is possible to do simply and manually.

So what do you pay for the above benefits? It seems that when you compare similar usable AH, perhaps in the region of two to three times as much.
(You can buy non-premium LiFePo at around $5.6/AH, but factor in that you can cycle 20%-90% as opposed to 50%-85%; also depends on the price you use for lead-acid, since there is quite a range).

Now, I do not have these installed yet, so it will be at least a couple of years before I could report on my real life experience, but we humans are ever optimistic.

John F

Hi John,
I just wondered how you managed a typical days recharging while at anchor. Is it done through the generator and does the generator do other tasks each day as well, for example making water or running the fridge.
So for example, run the generator in the morning for 1 hour while making water, then in late afternoon again for another hour making a total of 2 hours a day.
At the end of the final generator run, how full would the batteries normally be?

garry crothers

Does the paralleling of the 3 stage chargers not get confused by the higher voltages generated by the other chargers rather than the battery bank?
I’ve seen so much conflicting information on this subject, I’d be interested in your first hand experiencce



My Lifelines have done 4 seasons. Kind use with a 4 week vacation every year. The rest has been weekends and then back to the marina and the shore power. This year will be 6 month cruising. Much more demanding.

Honestly I do not expect the Lifelines to last longer than the Golf Carts open ventilated. Every battery expert that I have talked recommends open ventilated Golf Carts, if value for money is the only parameter. (Experts that offers both alternatives:-) )

I feel that the higher acceptance rate of AGM is only valid if you charge at the same voltage, 14.4V. Open ventilated can be charged with 14.8V which compensates for the lower acceptance rate. 0.4V makes a big difference.

But it is sure nice, not to have to deal with acid. Also it nice to know that the self discharge is low when you leave the boat in some odd place.

Stu Robertson

Great stuff…
I wonder if a battery desulphation unit might possibly reduce the need for frequent equilization…?

Steven Schapera

My boat is based in Sardinia, Italy. I replaced my two Lifeline AGM GPL-8D’s in July 2009. I subsequently had problems, which became progressively worse, relating to the batteries holding their charge. After emailing Lifeline in the USA, and communicating with them over a period of a week or so, they gave me the benifit of the doubt and arranged for their Italian distributor to replace BOTH batteries for NO COST! To say I was blown away is an understatement. Guess how many poeple I have told about this incredible customer service??? And guess what batteries I will always use? Yes, they are more expensive but they are the highest quality you can buy and the after sales service is the benchmark. Incredible!

Brian Wilkinson

With regard to your problem with obtaining a satisfactory charging regime from the alternator/regulator.
You have already sorted your mains chargers, so why did you not simply run an inverter from the alternator, and charge your batteries with the mains chargers connected to the inverter.
The alternator/regulator will maintain required output whilst ever there is a load such as the inverter attached, and your mains chargers will handle the tricky bits.
Easy to set this up to automatically switch from mains to inverter when the motor is running.
By now you are probably considering the advantages presented by the advancements that have been made in LYfePo4 technology.


I’m surprised you even continued with AGMs. Given the very poor life you are getting from them. I had AGMs on my last boat and I wouldn’t use them again. My current boat, a Hans Christian 38 has had the same gel batteries since 2003 and they still seem to be going strong. I never discharge them beyond the 50% point and they are kept topped off by a solar panels or by the Freedom 3000 whilst at the dockside

Matt Boney

Lifeline now say my absorption voltage can be 14.6 volts and the float at 13.4 volts. (Up from 14.4 and 13.2) Why have they made this change – is it just to keep up with competitors who are pushing up their charging voltages for a faster charge? What does Justin from Lifeline have to say on this?

Justin Godber

John is right. We are constantly doing testing. We have a labratory with 8 full time employees and 2 chemists that constantly test different things to improve battery life. Although 14.6 was not recommended prior it is now ok. Hope this helps. 13.2 to 13.4 is still recommended for float

Marc Dacey

John, I realize this post is about AGMs, but I was wondering if you held any opinions on lead-acid batteries. I am going to be purchasing and installing about a half-ton of them this summer, and I hear from sources I respect that the Trojan brand is not quite what it used to be, and furthermore, is overpriced as if it were an Apple product.

Not that there’s anything wrong with that!

In other words, although I have been impressed by Trojans in the past, I am not convinced they merit the price premium an owner with solid maintenance regimes and easy access would warrant. I could save hundreds getting a bunch of big ol’ Interstates, really.

I am considering buying six L-16 form factor batteries, 6 VDC, of about 370 Ah per ganged 12 VDC pair. This would form an approximately 1,110 Ah house bank, echo-charging an AGM 12 VDC start battery and an AGM 12 VDC windlass battery forward. Any guidance you may have would be appreciated.

Steve A

Hi Marc,
Trojan now has an L-16 RE-B 370 ah that has extra acid above the cells (good for maintenance and if heeled) and also has a deeper “mud rest” for sludge to settle into. It is a little taller than a normal L-16 at 17.5″. This is also available in a “golf cart” T-105-RE. I was told this is a battery that has been available for a year or 2. Sounds like good modifications of old technology.
Charles Industries has a new series of chargers that look interesting, the 93-ICM in 20, 40, 60, 80, 100 & 120 amp. They can be programmed to charge 4 battery banks at the same time, will charge 12 & 24 volt banks at the same time, and are designed to continue to work at reduced capacity (get home mode) in the case of partial charger failure. They also have programmable equalization modes. Have any of the engineers on this site installed and tested the output of this product, in particular the equalization program?

Marc Dacey

Thanks, Steve. Those are the very model of Trojan I was looking at. Your info suggests they are more thoughtfully designed than cheaper batteries, so I may have to revise my opinions.

Victor Raymond

Thank you again for an excellent post with plenty of sobering thoughts for us to ponder.
As I am lazier than most, I am always looking for the solution with the least amount of work, doubt and worry. We are seldom in a marina for more than 12 hours to go through customs etc. We also never hook up to shore power. We prefer to run our generator which we can barely hear even at night, (ask me how I know.) Which makes the prospect of equalizing particularly daunting and impractical however necessary for the life of the batteries. The only practical time for equalizing is when we are on the hard for extended periods.
I have the room and the structure to support a pair of very large, 280-320 watt solar panels, above my bimini. The disadvantage is the location would not suit angling towards the sun for maximum energy production, yet the large size may produce enough to keep the batteries charged up to max with an MPPT controller of course. This may have to be augmented with a wind turbine attached to aft radar post but I am hoping not.
We also have only provisition for 4 -4D’s at the moment although I too would prefer 4- 8D’s. We are a 24v boat so I am more of a disadvantage than you, I suppose. My refrigeration needs are less but probably similar in all other energy demands.
I guess the real question is can sufficient solar charging without regular equalizing keep expensive AGM’s from an early death?
Thank you in advance for your wisdom on this most troubling subject of all things nautical.

Barry Foster

IMHO 18 months is just not enough time to have figured out how to make AGM’s last. My experiance with them is very poor.
Go with the solar panels just laid flat on the Bimini. That’s how most are, and with the correct controller you should be able to equalize wet batteries. It takes little current to do this. But remember you are boiling the batteries to do this and the gases coming off are very explosive. I know this for a fact having been in a military battery charging room and seeing a lArge 24 volt batter explode covering all of us with sulphic acid
My choice is for gel cells. Mine have been on the boat since 03 and the three 8D’s are still going strong.

Victor Raymond

Thank you John, for your clarifying remarks. Yes the four 4D AGM’s are set up parallel and in series to make two banks at 24v each. Unfortunately that does little to boost up my AH near 800-1000 where I would like to be.
Given the battery box size I am just a little shy of being to put 4 8D’s in. I thought of one bank of 12 2v telcom batteries but then I only have one bank. And as you say it really limits my use during the equalization period.
From your comments and those of Barry, other than weight there are no downsides to the addition of large solar panels even if they are producing a fraction of their potential. The reason I can not articulate them is the boom has only a 6 inch clearance. Of course at anchor it is another matter.
Thank you again for your comments.


John, the AGM’s that I had told me not to equalize although a different service tech said that I could. The question that I have is ” if AGM’s are not liquid, how can they sulphate where the sulphate shorts the plates out on a lead acid by sink inking to the bottom off the battery”?
AGM’s can be installed in any position, even upside down, so it it difficult for me to see how they sulphate.
Additionally they are totally sealed so a equalization could lead to a battery bursting. Not good. I personally have seen a AGM bulging during a eqalization cycle.
As you well know deep discharge, below 50%, or 12 volts for most people, is a certain way to terminate any battery of any type.


Hi, I have read all the comments here, I two have a electronics background spanning back to a apprenticeship in 1960. I never specialized in batteries, however I read a lot.
Your time frame of your AGM’ is just not enough to establish long term results.
I notice that Lifeline comment direct on this site so am I to assume you have a relationship with them?
My comments are purely based upon personal experience and not just a opinion.

I thank you for a very informative site and sharing your experience with me and others, so before I get into a fight with you this will be my last comment and I shall unsubscribe
Many thanks

John Pedersen

Hi John,

I’ve arrived at similar conclusions as yourself – the importance of equalisation and also having two battery banks so that one can be using a small amount of power from my solar panels to fully charge, while the bulk of the power from the panels goes to the other battery. Most charge controllers on the market seem to suggest you can fit and forget them, and this is often what cruisers do – and then they have to replace their batteries frequently.

I have much smaller power requirements than you, so I manage fine with just a couple of solar panels. However, my controller doesn’t allow me to take the equalisation voltage up to the manufacturer’s recommended voltage, so I currently do equalisation by connecting my panels directly to the batteries and frequently adjusting the voltage by slightly shading the panels as necessary. It is quite a bit of work though, and your regime seems quite onerous too, so I’m wondering, why no mention of lithium batteries?

I have no experience with lithium. But from what I’ve read, lithium batteries can soak up pretty much any power you throw at them and you don’t have to taper the charge as they fill up. This would remove the need for two battery banks. I know they are a lot more expensive, but since they can absorb energy so much more quickly, I think money could be saved on having to have fewer solar panels etc (as they’d be running at closer to full capacity rather than sometimes having to cut back to provide a tapered charge. And then there’s the weight saving…



I just spoke to Dave at Lifeline batteries, and he said they are back to recommending 14.4 and 13.2 (for absorption and float), not the higher voltages (14.6 and 13.4) they though were okay a couple of year back. John, perhaps you can find out what changed?


Hi John
I’ve just re-read the series to feed thinking about improvements to our entire charging setup. Invaluable insight, many thanks!
5 years on now – how are your batteries fairing ?