The Offshore Voyaging Reference Site

11 Steps To Better Lead Acid Battery Life

Battery car

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

JHH5-12590#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:

  1. Batteries like to be charged hard until they are fully charged.
  2. 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.
  3. 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.

More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—Part 1, BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Part 2, Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Part 3, Current (Amps) Requirements and Optimal Voltage
  33. 11 Steps To Better Lead Acid Battery Life
  34. How Hard Can We Charge Our Lead-Acid Batteries?
  35. How Lead Acid Batteries Get Wrecked and What To Do About It
  36. Equalizing Batteries, The Reality
  37. Renewable Power
  38. Wind Generators
  39. Solar Power
  40. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  41. Battery Monitors, Part 1—Which Type Is Right For You?
  42. Battery Monitors, Part 2—Recommended Unit
  43. Battery Monitors, Part 3—Calibration and Use
  44. Battery Containment—Part 1
73 Comments
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Norris

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

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

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 Armitage

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!

Kettlewell

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.

Kettlewell

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?