In the last chapter, we quantified how short battery life will be on a cruising boat with a standard electrical system, now let’s move on to fixing that.
This Applies to All Lead Acid Batteries
AGM, gel, liquid filled and carbon foam are all lead acid batteries with the same basic chemistry and they will all fail if we don’t treat them properly. So the following list will help any liveaboard voyaging sailboat owner get longer battery life.
Just to be clear, none of this applies to lithium batteries, which we cover later in this Online Book.
Commonly Known Stuff
The first three rules are known by most liveaboard voyagers. But if they are all we do we will go through a lot of batteries. 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 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. Lead acid 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
#4 Make sure you have access to shorepower 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 shorepower charger on for long periods.
There are some AC chargers that are smart enough not to damage your batteries by being left on for long periods but they are few and far between. And that indictment includes most of those that claim to be three stage, all singing, all dancing, etc.
#6 Only buy batteries that can be equalized.
Remember rule #3 that none of us liveaboards can really follow? Regular equalization is the next best thing.
#7 Equalize your batteries once a month or so.
We explain how later in this Online Book
#8 Install a truly smart alternator voltage regulator.
For most of us live-aboard voyagers, or at least those like us who are way too 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 from the factory setting and even then, not very well. We recommend a good regulator later in this online book.
#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).
We have three chapters later in this Online Book to help you choose a monitory system and calibrate it so it’s actually useful.
#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 gels 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 first two chapters of this online book.
But here’s 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 2% to 0.5% (varies by type) 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.
Up Next
Read on in this Online Book for detailed how-to chapters on all of the above.
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
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.
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!
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.
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!
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!
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.
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.
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?