Eight months ago we replaced our house battery bank for the third time in four years. Concurrently we started a project to improve the life of those batteries—like anyone would after going through the kind of coin we have replacing batteries!
A month ago we reported that our new batteries—generously provided for free by voyage sponsor, Lifeline Batteries—were showing dramatically better performance than their predecessors due to the changes we had made in how we cared for them.
We wrote about those changes in mind numbing detail in a series of posts. Now we will give you the summary, together with a couple of details not yet revealed.
It’s Not Just About AGMs
But before we get into the specifics. This project started off as a test of AGM batteries on a live-aboard sailboat. But one of the first things we learned is that it really does not matter whether you buy AGM, gell, or liquid filled batteries. They all use the same basic chemistry (lead-acid) and they will all fail quickly if you don’t treat them properly. So the following list will help any live-aboard voyaging sailboat owner get longer battery life.
Commonly Known Stuff
The first three rules are known by most live-aboard voyagers. But if they are all you do, as we did prior to this project, you will go through a lot of batteries, just like we did. Still, they bear repeating:
#1 Don’t regularly discharge your batteries over 50% of rated capacity.
Breaking this rule occasionally is no big deal, but if you break it regularly be prepared to replace your batteries often…really often.
#2 Charge your batteries back to at least 80% of capacity after every discharge cycle.
It’s also important that you do this sooner rather than later. On no account should batteries sit for more than a day or so in a deeply discharged state. Typical AGM battery banks will be close to this 80% status when the charge current (amperage) starts to drop below the maximum that a well regulated alternator or AC charger can supply at the proper acceptance voltage (typically about 14.4 volts).
#3 Charge your batteries to 100% as often as you can.
Now we are getting to the hard stuff. Battery manufacturers really want you to charge your batteries to 100% after every discharge. But that is simply not practical for us live-aboard voyagers because although we can honour Rule #2 in an hour or so with good charging equipment, getting to 100% typically takes another five hours! Still, do it as often as you can—read on for how.
The New Stuff That is Saving Our Batteries
#4 Make sure you have access to shore power for at least a week after installing new batteries.
The reason is that batteries when shipped from the factory are not “fully finished” and it takes several discharges, followed by charges all the way to 100% to bring them up to 100% capacity.
By the way, you do not need to “form” new batteries by fully discharging them and then recharging them as some “pundits” will tell you.
#5 Don’t leave a shore power charger on for long periods.
There are a some AC chargers that are smart enough not to damage your batteries by being left on for long periods, but very few. And that indictment includes most of those that claim to be three stage, all singing, all dancing, etc.
More on how to tell how smart your charger really is, or more likely, is not.
#6 Only buy batteries that can be equalized.
Remember rule #3 that none of us live-aboards can really follow? Regular equalization is the next best thing .
#7 Equalise your batteries once a month or so.
#8 Install a user-programmable alternator voltage regulator and reprogram it to actually fully charge your batteries.
For most of us live-aboard voyagers, or at least those like us who are way to0 cheap to spend a lot of time in marinas, the one and only time we will get to fully charge our batteries will be when doing a longer passage under power. The bad news is that most alternator voltage regulators, yes even the expensive three stage ones, won’t do the job unless reprogrammed.
#9 Install a smart measurement system and use it.
Contrary to what many manufacturers will tell you, this stuff is generally anything but “fully automatic”. You need to skipper your charging system, just like you skipper your boat, and to do that you need to know what’s going on.
Minimum acceptable measurement capabilities:
- Volts at the battery (requires a wire going to the battery positive post).
- Amps going into the battery (requires a shunt).
- Amp hours going in and out of the battery (requires a shunt).
#10 Install an alternator regulator and AC charger(s) that have temperature measurement probes on the batteries.
The reason is that the proper voltage to charge and equalize batteries varies with temperature. This feature is particularly important for sealed batteries like gells and AGMs.
#11 Know how your batteries should be charged and how to tell they are full.
There is more inaccurate information about this out there than just about any area of cruising knowledge. And yes, to really understand the real facts, you’re going to need to read all that mind numbing detail I mentioned—sorry. But here is the short version:
- Batteries like to be charged hard until they are fully charged.
- Batteries are fully charged when the current (amps) they are accepting at their specified acceptance voltage—typically about 14.4 volts at 70f (20c), but check with the manufacturer—has dropped to 1-2% of their total capacity measured in amp-hours. This is the only practical way to know that they are 100% charged.
- At that point, and at that point only, the charge voltage should be dropped to the float level, typically about 13.4 volts.
Summary
Sure, there are a lot more things you can do to improve battery life: wind and solar power (if used correctly), and complex and expensive fully automated systems, to name just two.
But these eleven steps are all you really need to do to get the dramatically improved battery performance that we are enjoying on Morgan’s Cloud.
Norris February 11, 2011 at 9:22 am
Hi,
Thank you for the great in depth series of articles on batteries. Your website has the feel and reputation of providing rock solid, practical, objective and detailed information. Consequently, I look forward to every e-mail notification.
Regards,
Norris
David Head February 11, 2011 at 9:37 am
All very useful, and for me quite poignant! Late 2010 one battery in a bank of 5 started to overheat whilst charging. In time I replaced all batteries and verified that the battery charger was correctly set for the batteries we had installed. The setting was wrong and was the root cause of the early melt down. This is easily ignored when changing batteries. Additionally, in my case I have dispensed with any split charging system, preferring to use the Blue Seas 7610 SI battery combiners that very accurately determine which/when to charge, and when to isolate the batteries. I would commend this system as an alternative to the dubious claims made by all manner of battery split-charging devices. It proved to be easy to wire up, and has worked very well.
Chris February 11, 2011 at 10:15 am
Excellent, Excellent
I would like to reiterate a point I made earlier as to temperature sensors and temperature compensation.
Make sure you understand sensor failure modes, and have some means of compensating for the failure — particularly if the boat is left unattended.
Most (actually, I think it is “all”) report a battery temperature of 0 deg F in the event of a failure. The higher the battery temperature when this occurs, the worse the impact. For us it meant 15+ volts delivered during Acceptance to a 90 deg F battery (and a resulting $1500 loss).
Make sure your temp compensated source also has the ability to specify a “not to exceed” voltage.
If not, I would recommend setting the charge source for the highest battery temperature expected during an absence, and adjust for the possible under-charge on return.
Again, excellent advice, thanks John!
John February 11, 2011 at 8:58 pm
Hi Chris,
A really good point. This is just another reason why we on “Morgan’s Cloud” keep a careful eye on what our chargers and alternator are doing using our Link 2000 meter.
Unless there is a really good reason (very rare) we don’t leave our AC chargers on when we are not on the boat either. Aside from the danger of ruining the batteries, you can burn your boat if a cell shorts in one of the batteries and you are not there to shut things down when you smell burning.
John Armitage February 11, 2011 at 2:18 pm
Hi John, a great series, very useful. However, this statement: “But one of the first things we learned is that it really does not matter whether you buy AGM, gell, or liquid filled batteries” could be interpreted ambiguously. It is true concerning how to treat batteries, but it is not true in evaluating the cost/performance/convenience trade-off in choosing between types of batteries to buy. As you know, it matters a lot!
John February 11, 2011 at 9:41 pm
Hi John,
Good point. My statement was in relation to these 11 rules, not the issues of deciding which battery type will best meet a given need and price point. That’s a whole new set of posts!
Kettlewell February 11, 2011 at 4:10 pm
Excellent series of posts! One thing I am still not certain of is how to make rapid, maximum possible charging foolproof so you don’t burn the boat down, as has happened to several folks I know of. Inherent in the process is generating lots of heat and possible gasing of explosive vapors in an enclosed space. A recipe for danger.
Also, I am not sure about this statement: “Batteries like to be charged hard until they are fully charged.” I suppose it depends on the definition of “like,” but my understanding has always been that fast charging shortens a battery’s life.
John February 11, 2011 at 9:18 pm
Hi John Kettlewell,
Thanks for the kind words.
I have it on pretty good authority (Justin at LifeLine) that their batteries, at least, have, in exhaustive testing, shown that they actually last longer if charged at high current (amperage). This helps to stop them sulfating, which is usually how boat batteries die.
In fact LifeLine are quite happy to have their batteries charged at currents up to a number equal to the capacity of the battery in amp hours. In other words, our two 8Ds could take 240 amps each, or a total of 480 amps without damage or overheating–way beyond what most alternators or wiring could possibly produce.
The key parameter is not the number of amps going in, since the battery’s own internal resistance will limit that (ohms law) but rather that the battery’s maximum acceptance voltage is not exceeded (generally about 14.4 volts at 70F). Also, Rule 10 is important to prevent overcharging as the battery heats up from charging since internal resistance drops.
In summary, the old idea that batteries like to be slow, or even trickle charged, is, I am really pretty sure, simply wrong.
Kettlewell February 11, 2011 at 9:56 pm
I realize they aren’t Lifeline AGM batteries, and they are a different technology, but the new electric cars all seem to suffer degraded lifetimes if you do a lot of fast charging. Here’s one article on the subject: http://green.autoblog.com/2010/05/27/details-on-nissan-leaf-battery-pack-including-how-recharging-sp/
I understand AGM batteries can withstand higher charging currents, but does that mean that is ideal?
Beth Anderson February 11, 2011 at 6:44 pm
Very helpful article. As I read, I kept wanting to add “or use solar panels!” to every mention of shore power. We installed a bank of four house batteries and four solar panels on our boat before embarking on our 6 month cruise in 2009. We removed two of the panels last spring when we returned to the US and have never used shore power. All of the house batteries are still going strong. In the Caribbean our bank was typically fully charged by noon each day. While I realize that four solar panels might be overkill for some people, it was awesome to not have to worry about our battery strength. There was only 1 occurrence I remember where the battery strength dipped below 50%.
This year we are finally removing the other two panels and switching to shore power at the marina. I’ll make sure we follow this guide to ensure that our batteries continue to survive.
John February 11, 2011 at 9:32 pm
Hi Beth,
Really good point on how solar can help. Our problem is that, in large part due to the computer demands of this site together with our publishing efforts (Norwegian Cruising Guide), our usage is up around 250 amp hours a day.
To satisfy that load, or even make a dent in it, with solar would take a lot of panels. And the big issue for us is where to put so many in a seaman like way–we absolutely abhor deck clutter. More on that in a coming post.
Chris February 11, 2011 at 7:10 pm
Beth, I would be interested in knowing the panel sizes and bank size. I just installed 3 Kyocera 135s to service a 660 Ah bank. The results on the tail of the season were excellent, usage was light to moderate. Thanks, Chris
Ben February 12, 2011 at 5:18 am
I have found these articles very good, thank you John. It certainly makes me appreciate my simple system, but has given me some ideas for improvements. I use standard wet cells, but have only about 140 amp-hours capacity. My main charging system is two (soon to be three) 40W solar panels. They work through a reasonably smart regulator/battery monitor that has an equalization cycle. For more info about my setup see http://snowpetrelsailing.blogspot.com
I have found this to be a good and simple system for my boat. But then I have no fridge and have to be a bit careful with power. I rarely have to run the main engine for power, normally only if I am using the big inverter with power tools. My batteries have lasted 6 years, but are pretty stuffed now.
I can relate to the desire to keep clutter on deck to a minimum but accept this trade off for the safety of having a truly independent power supply. My third panel will be removable so I can store it below in a serious blow.
Cheers
Ben
John February 15, 2011 at 11:43 am
Hi Ben,
Thanks for the comment. Just to clarify, I don’t have a problem with one or two solar panels well secured in an out of the way place like you and Colin have (see this post). But to make a dent in our considerable power use, we would need a whole bunch of panels festooning the boat, which would not be seamanlike, particularly given the places we go.
Steve & Rebecca February 12, 2011 at 9:59 pm
Congratulations John, I have really appreciated these articles and the light that they have shed on an often misunderstood subject.
Before anyone believes that the wheel has been re-invented however, can I just caution that the conclusion this article is leading to is pretty much what serious battery maintainers have known since WW2.
The issue that John has identified (correctly and thankfully) is that the purveyors of certain battery control equipment have, for some years now, ‘pulled the wool’.
The battery care system that John is now leaning towards is, as he rightly says, based on the fact that most modern batteries (despite the fancy labels) are simply variations on a simple chemical equation.
I hope that the discussion progresses to more detailed issues regarding equalisation (for example ventilation and hydrogen percentage monitoring during that process) and whilst not quite as important, quarterly (or similar) discharge which is almost the mirror image of equalisation.
Then we may be getting somewhere (without the fancy bits).
Steve
Anthony Gilbert February 24, 2011 at 12:38 pm
Just wait until you get a taste of “Lithium Bromide” batteries. This is in the experimental stage now for next generation autos.
Tom Schaefer March 15, 2011 at 4:29 pm
John, first thanks for the excellent series of emails. Yesterday I ordered five Group 31 Lifeline AGMs here in New Zealand (four house and one starter – constrained to Group 31s by the location of the batteries). Your work and research will hopefully lead them to have a long and happy life.
Question on leaving batteries on float (as when at a marina). Is there any way to do this safely? We are using a Mastervolt MassCombi inverter/charger with adjustable (via a computer link) charging and float voltages.
Thanks
Tom
John March 16, 2011 at 9:32 am
Hi Tom,
In answer to your question, I guess it really depends on whether you mean safe for the batteries, or safe for the boat. If the former, then the answer is yes, as long as you either have a shunt that allows the charger to measure actual amps going into the battery, so that it can determine when the batteries are fully charged and drop back to float voltage (typically around 13.4 volts) from acceptance voltage (typically around 14.4 volts) without being confused by loads. You can also do this manually. This is all explained in this post.
However, if you mean safe for the boat, then our answer would be no, not really. Any time you charge a battery there is the potential for fire if one of the cells in that battery shorts out. So, for us on “Morgan’s Cloud”, we don’t leave any batteries charging unattended if we can help it. We don’t even leave the rechargeable AA batteries that we use in our photography strobes and flashlights (torches) on charge when we are not around to keep an eye on things. In fact we have a friend who lost his house when an AA battery charger caught on fire when he was out.
Of course this second point may just prove how totally anal retentive we are, rather than that there is a real risk!
I just don’t have enough data on fires started by batteries charging to know for sure. But I think we have someone who visits this site regularly who can give us some real engineering information on this.
Matt, are you out there?
Matt Marsh January 29, 2012 at 6:13 pm
You talkin’ to me, mate? (Sorry I’m late….)
I don’t have any statistics on how often marine battery chargers start fires.
Regarding Chris’s broken temp sensor causing his charger to cook the batteries: Returning a reading of “0″ when the true condition is “no clue” is wrong; control systems are generally supposed to have a fault condition that is easily distinguished from an extreme but correct reading.
I have no idea how such a flawed design could have passed QA, but an awful lot of junk does sneak through, even if it has fancy brand names and high price tags. Caveat emptor; unless you actually wire the thing up on a test bench and force it into fault states, it’s hard to tell what it’ll do.
If autonomous operation is important to you, then by all means, feel free to pay for it. Put two extra thermocouples on each battery and use them to drive redundant logic circuits that’ll cut off the power if anything gets too hot. Have alarms and interlocks for main bus overvolt and main bus undervolt conditions. Have an alarm and independent cutoff for the charger over-current condition. Have a thermal interlock in the shore power inlet.
If you don’t want to install and integrate all those sensors and interlocks, simply turn all high-power equipment off when you leave the boat.
(I would have no qualms about leaving a 2 amp trickle charger unattended, but anything that is able to cause an overload should either have a fully independent emergency interlock system, or should be shut off when unattended.)
John January 29, 2012 at 6:43 pm
Thanks, Matt. Great information as always.
Chris March 16, 2011 at 10:08 am
Clearly, I’m not Matt, but I can tell you we had the temp sensor for our charger fail while away from the boat and float charging.
The sensed voltage went to zero, and the supplied voltage was accordingly bumped up by the firmware to 15+ volts– appropriate for a temp of zero, but not for a temp of 90 deg F.
The result was $1500 of Dekas destroyed, and H2S contamination and damage throughout the boat. One battery had boiled and had begun swelling…
More details are available in a comment made on 11 Feb (see above) and in prior posts.
John March 16, 2011 at 11:41 am
Hi Chris,
Thanks very much for bringing this up. I had a senior moment. I should have linked to your original comment.
I’m just hoping that Matt may have some industry statistics or engineering theory that will back up our gut feel that unattended battery chargers are an unacceptable fire risk.
Chris March 16, 2011 at 11:49 am
No worries, I figure I have earned every single senior moment that chooses to have me.
Colin April 13, 2011 at 4:50 pm
John,
Thank you for this lucid, practical series. We have a Balmar 612 and a house bank of Lifeline AGMs, being replaced this spring. Here’s hoping they live a long life!
Do you have any update on the manual settings to your Balmar 612? Specifically, are you still using the 2 hour minimum setting for the absorption stage, and the 40% field voltage for the transition to float? Also, I am curious as to the logic of choosing 40% field voltage… Did you simply take 1.5% of your battery bank capacity in amp-hrs (definition of a charged battery) and add this to your average electrical systems demand while motoring?
John April 15, 2011 at 6:49 pm
Hi Colin F,
We have made a few more small adjustments on the Balmar regulator since the original post but I really don’t want to get into publishing them as a recipe for success since each boat will be different. For example, we often turn on our fridge that draws 60 amps just before the regulator is about to go into float mode to keep it in acceptance for another hour or so if our batteries are not fully charged.
The key is that you need to monitor how your regulator is working on your boat with your batteries and typical loads and then slowly tune the settings to do the best job of fully charging your batteries without overcharging them excessively.
As to the 40% of field voltage. That was just a starting point that we tried. There is just no scientific way to calculate it since different alternators will put out different amounts at a given field voltage setting.
In summary, there really is no other way than trial and error for each boat. And even after you get it about right, it will be important to keep monitoring what the charger is actually doing. I think that this is why Balmar sets their regulators so conservatively when they ship them. Higher settings would overcharge some boats and undercharge others. So they go for settings that undercharge just about everyone–understandable in our litigation filled world since overcharging can, in rare circumstances, cause a fire!
Reed Koch August 30, 2011 at 6:00 pm
Have you considered a whispergen? There are some downsides like there is only one manufacturer of Stirling powered generators however it would seem idea for your type of application. In comparison to a diesel engine it’s very efficient even at low output and it’s quiet. You could set it to charge every night when you went to bed and in the morning you would be fully charged. With the low nighttime load it would “see” the correct amperage going into the batteries.
John September 2, 2011 at 2:25 pm
Hi Reed,
Thanks for the great suggestion.
Yes, I have looked at the Whispergen Stirling engine and on the face of it it solves many or even all of the problems with charging batteries on a cruising boat. However, we have a policy of only installing mainstream technology on “Morgan’s Cloud”.
With the places we go we just can’t afford to experiment.
Dave October 18, 2011 at 11:06 pm
An interesting comment by Ample Power ( http://www.amplepower.com/phpBB3/viewtopic.php?f=3&t=311 ) saying that with their testing they couldn’t recommend AGMs.
John October 19, 2011 at 9:49 am
Hi Dave,
Thanks for the pointer. I think the key point is that they had not had an AGM battery manufacturer come up with a recommended protocol. But we have exactly that from LifeLine batteries and since we have applied it we are getting great service from our AGMs.
Having said that, AGMs are not for everyone or without disadvantages. But if you want faster charge acceptance and zero self discharge, as we do, they are worth considering.
John Robinson January 9, 2012 at 2:00 pm
John: How is the AGM battery test going?
John January 10, 2012 at 10:56 am
Hi John,
Coming soon to a web site near you.
John Armitage January 11, 2012 at 12:11 am
I found Ample Power’s dis-recommendation of AGM batteries interesting, since I have been getting excellent service from my Lifeline AGM batteries under heavy deep cycle use, presently still healthy at 5 years which is double what I got from West Marine gel batteries under the same usage conditions before they died. Note that the Ample Power tests were ‘years ago’, and all brands of AGM are not necessarily the same. To condemn the whole technology on these old and limited tests is not realistic.
Also, I would say that deliberately discharging to 10.5 volts (100% discharge) constitutes misuse; it may be (or not) that some or all AGM batteries are more sensitive to this sort of misuse than a regular flooded battery, and the use must decide if this is relevant.
Dennis Fechner February 2, 2013 at 5:55 pm
What is interesting is to see how the Prius makes its batteries last for so long. As I understand it, they always run the batteries between a range of something like 60% to 80%…or never fully charged and never less than 60%. I have gel batteries, two 4D’s which I ran them at basically the above levels most of the time and they lasted 13 years before they had only about 50% capacity left so I bought new ones. I have a Rival 32 and sailed from Seattle to La Paz 9 years ago. Perhaps the Prius batteries are very different but my experience bares some of this approach out. I did leave the boat in storage at about 90% charge without a charger and came back 6 to 7 months later and could still start my diesel engine as the charge was above 12 volts. Amazing but true.
Perhaps Gels are different than than the absorbed matt batteries you are talking about. I had a best friend who ran a charter service out of La Paz and had gels on his boat that lasted 10 years under charter service and living aboard full time.
I had another friend who had the absorbed matt batteries and he had the same problem you had…they did not last and he was going back to gels.
I had another smart friend who went from Gels to Lifeline Abs. Matt and he was very unhappy with their short life and was going back to gels.
I am not in the marine business except I worked at a boatyard in Seattle for 10 years and saw all kind of things that should have worked, not work. I have nothing to sell to anyone but these are just my personal experiences and those of my good friends who are good sailors.
I love your site…it is one of the best ones on the web. The way you think is what I like especially for heavy weather. I wish you well with the batteries you choose. It will be interesting to see if they can last 8 to 10 years.
Best Regards,
Denny
John February 3, 2013 at 10:40 am
Hi Dennis,
Thanks very much for the kind comments
Also, thanks for the interesting comment. A few thoughts:
Dennis Fechner February 5, 2013 at 7:15 pm
Hi,
No, there is no way to equalize a gel but my friends who lived aboard and chartered full time, with high energy demands (the used five 4 D’s) had them last 10 years so maybe they don’t sulfate the same way as AGM’s. He also had 4 large solar panels working all the time and he like I set the solar regulator it at about 13.9 to 14.1….not the 14.3 it came at.
My alternator on my Volvo 2030 came from the factory set at 14.1 which is the other reason I use Gels and so far happy as a clam.
But for sure, your demands on your batteries is much, much greater than mine so I do hope they finally work for you as I think AGM’s can be charged at a faster rate than Gels which is appealing even to me.
I really appreciate your site. The gear that works is such a great part of your site and I appreciate it a lot. You give such well reasoned advice/reviews which is easy to understand. Thanks for all your research as well!!
Regards,
Denny