We have written about battery charging in mind numbing detail in this Online Book. Now we will give you the summary, together with a couple of new tips not yet revealed.
It’s Not Just About AGMs
This project started off as a test of AGM batteries on a liveaboard sailboat but one of the first things we learned is that it really does not matter whether you buy AGM, gel, 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 liveaboard voyaging sailboat owner get longer battery life.
Commonly Known Stuff
The first three rules are known by most liveaboard 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 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 liveaboard 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
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.
#8 Install a user-programmable alternator voltage regulator and reprogram it to actually fully charge your batteries.
For most of us liveaboard 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.
#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 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 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 0.5% 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.
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.