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.


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.

Like what you just read? Get lots more:

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  1. One Simple Law That Makes Electrical Systems Easy to Understand
  2. How Batteries Charge (Multiple Charging Sources Too)
  3. How Hard Can We Charge Our Lead Acid Batteries?
  4. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  5. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  6. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  7. The Danger of Voltage Drops From High Current (Amp) Loads
  8. How Lead Acid Batteries Get Wrecked and What To Do About It
  9. 11 Steps To Better Lead Acid Battery Life
  10. 10 Tips To Install An Alternator
  11. Stupid Alternator Regulators Get Smarter…Finally
  12. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  13. Smart Chargers Are Not That Smart
  14. Equalizing Batteries, The Reality
  15. Battery Monitors, Part 1—Which Type Is Right For You?
  16. Battery Monitors, Part 2—Recommended Unit
  17. Battery Monitors, Part 3—Calibration and Use
  18. Do You Need A Generator?
  19. Efficient Generator-Based Electrical Systems For Yachts
  20. Battery Bank Size and Generator Run Time, A Case Study
  21. Battery Options, Part 1—Lithium
  22. Battery Options, Part 2—Lead Acid
  23. Why Lithium Battery Load Dumps Matter
  24. 8 Tips To Prevent Lithium Battery Load Dumps
  25. Lithium Ion Batteries Explained
  26. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  27. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  28. Q&A—Are Battery Desulphators a Good Idea?
  29. Renewable Power
  30. Wind Generators
  31. Solar Power
  32. Hydro Power
  33. Watt & Sea Hydro Generator Review
  34. A Simple, Efficient and Inexpensive¹ 12 or 24 Volt DC Electrical System
  35. 8 Checks To Stop Our DC Electrical System From Burning Our Boat

John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for 25 years, first in yachting magazines and, for the last 20 years, as co-editor/publisher of AAC.

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