Don't Kill That New AGM Battery

Posted by Darrell Nicholson with Rod Collins at 04:47PM - Comments: (19)

One of our test batteries that had a rated capacity of 105 amp hours lost nearly 30 percent of its capacity after our series of 30 deep cycles (below 50 percent state of charge) and partial recharges. The optimum state of charge (no load) we could achieve after the test and after fully recharging is shown registered here on the constant load capacity tester— 73.4 amp hours.

Battery manufacturers want their batteries recharged to 100-percent state of charge after each discharge. In reality, few cruising boats (or any boats kept on a mooring) return their batteries to 100-percent state of charge after each cycle. This typical battery use, or abuse, is called partial state of charge operation, and if it continues, a sailor can see his AGM battery perform noticeably worse than a less costly, deep-cycle flooded battery bank. This isn’t the battery’s fault; it is just a lack of understanding of how to properly care for an AGM battery.

In 2015, we carried out a comprehensive update of our 2006 test of “sealed” valve-regulated lead acid batteries also known as either gel or absorbed glass mat batteries. For the more recent test of partially charged AGM batteries, Rod Collins of Compass Marine and marinehowto.com and Marine How To.com cycled five different batteries through 30 deep cycles (to below just 50 percent state of charge) and then put them on the charger for one hour to demonstrate just how quickly a cruising sailor can ruin a good battery. Even after just thirty of these cycles, some of the new absorbed glass batteries in our test never fully recovered to their pre-test capacity.

Here are some tips that came out of our test that can help you prolong the life of your AGM battery.

  1. Charge to full as often as possible, this point cannot be over emphasized.
  2. Get back to at least 80-85 percent state of charge (full capacity) with each charge cycle and get to 100 percent state of charge as soon as you can thereafter. 
  3. Don’t regularly discharge your bank below 50 percent state of charge.
  4. Size your most powerful charge source, usually an alternator or inverter-charger, for a minimum of 20 percent of bank capacity. Odyssey TPPL AGM’s prefer 40 percent of amp-hour capacity as minimum charge current.
  5. Use smart chargers. Not all chargers that claim to be smart are in fact smart.
  6. Use temperature compensated charging for all charging sources.
  7. Use smart solar controllers. Some solar controllers start each new day at a new absorption voltage charging cycle. This is not healthy for AGM batteries that have low self-discharge and minimal parasitic loads when left unattended on-the-hook. Smarter controllers have a voltage trigger to pop them out of float mode. If they don’t drop to the trigger voltage they remain in float.
  8. Using the correct float voltages are a critical aspect of AGM batteries. Chargers that use “dip switches” for programming often lack the correct voltages for both absorption and float settings.
  9. Use an alternator temperature sensor and external regulator if possible. AGM batteries can demand a lot from an alternator and the heat created can shorten its life or cause premature failure.
  10. For the best charging performance minimize the voltage drop in system wiring.  Even a 3 percent voltage drop at 14.4 volts means just 13.96 volts at the battery terminals. Incorrect voltage sensing robs you of the fastest charging potential, especially during short duration, high current charging events.
  11. Know your correct state of charge at all times. If this means investing in a battery monitoring device it will help in overall cycle life. If you are using voltage to determine state of charge be sure you are getting it as accurate as possible.
  12. Avoid installations in engine rooms or hot areas of the boat. Heat shortens battery life.

     

Comments (19)

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Posted by: Adrainsmith | December 21, 2018 5:30 AM    Report this comment

Regarding this statement:

Size your most powerful charge source, usually an alternator or inverter-charger, for a minimum of 20 percent of bank capacity.

For most boats this is not remotely possible. 600AH bank would require 120 amps going in to equal 20% of capacity. Nobody I know has a 120 amp shore power charger or alternator.

Our last set of Rolls lasted 8 years with moderate to hard use, using 100 amp chargers and 15 amps of solar.

Posted by: Pelican5077 | August 19, 2018 11:29 AM    Report this comment

Great topic but your review presents a glaring deficiency:

Why would you not include Carbon Foam AGM's (Firefly) in your testing? After all, these were specifically designed to allow for extended and repeated deep discharges and prolonged partial state of charge; more or less the exact torture test of a working boat on a mooring or while cruising.

This would have been be a great opportunity to see if they live up to the promised performance improvements.

Disappointing...

-evan

Posted by: eheffa | August 19, 2018 11:13 AM    Report this comment

Thanks very much for this input...seems with my particular relatively limited requirements (I do have a refrigerator but we do not use it, we pack ice into a small cooler), three batteries seems overkill and maybe a single AGM a little bit bigger than a group 27 might be all I need...?

Posted by: adrift | August 17, 2018 10:21 AM    Report this comment

I have had two AGM batteries on my trimarans one on each boat. The first battery, a West Marine, lasted ten years. The second, a Lifeline, is nine seasons old and going strong. Both boats use outboards for auxiliary propulsion. They have unregulated 6 amp charging systems. This is combined with solar panels and charge controllers. Currently I have a group 31 AGM, 140 watts of peak solar power, plus the outboard on occasion charges the battery. This setup runs a small Dometic fridge 24 hours a day, all season, plus it starts the engine, runs the electronics, the tiller pilot, and charges the 28 volt drill used to winch up the main. My conclusion is that the battery is at close to full charge most of the time. The solar panels charge the battery slowly. The fridge with its low voltage cut off drains the battery a bit but not excessively. It seems that for one AGM, this simple slow charging system to the float voltage works well. I leave a solar panel connected all winter to keep the battery charged. In New England, regular lead acid batteries seldom last ten years on similar trimarans. I find the AGM the optimal solution if weight is not a consideration. Some of the similar trimarans have switched to LION of some sort with the electronic systems to control them. They tolerate being discharged below 50%, but for me the cost and complexity outweigh the benefits.

Posted by: RT | August 17, 2018 9:26 AM    Report this comment

I am new to this side of sailing, meaning I had smaller boats with only a small engine and no batteries in the past. But, I bought bigger recently. I have one group-24 wet and two group-27 AGM batteries. I am on a mooring all the time. I have a NEMA 2000 plot charter from Garmin, two transducers under for speed/depth, and one wind transducer. Other than these, there is the radio. We are two hours drive time from the boat so only get to it once a week. Once there, I motor for 20-30 minutes out, sail and then motor 20-30 minutes in, in order to keep the batteries charged (I think, but as I said, I do not really know what I am doing because I am new to this and relying on what the yard said was OK to do). Diesel, Westerbeke 12 HP. Do I really need all three batteries? Would only one AGM suffice? Is there a forum someone could point me to so I can learn? I am after all of the information possible that anyone is willing to teach. Thank you.

Posted by: adrift | August 17, 2018 8:29 AM    Report this comment

Regarding this: Size your most powerful charge source, usually an alternator or inverter-charger, for a minimum of 20 percent of bank capacity. Odyssey TPPL AGM's prefer 40 percent of amp-hour capacity as minimum charge current.

How is this even remotely possible? We have 600AH of Rolls AGM batteries (brand new, 8 years out of the last batch). 20% of that is 120 Amps. We use a Magnum charger/inverter that will theoretically deliver 100 amps and a Balmar alternator that will do the same (although we can only run it at 75% or it will overheat). We can combine solar and charger at the dock and achieve 120 amps, but eventually this will overheat the batteries and the charger will shut down. For most boats, delivering 20% of bank capacity cannot be achieved for a battery bank larger than 500 amps, and even then doing so puts a 100 amp shore power charger at maximum capacity.

Am I missing something?

Posted by: Pelican5077 | August 16, 2018 10:36 PM    Report this comment

Regarding this: Size your most powerful charge source, usually an alternator or inverter-charger, for a minimum of 20 percent of bank capacity. Odyssey TPPL AGM's prefer 40 percent of amp-hour capacity as minimum charge current.

How is this even remotely possible? We have 600AH of Rolls AGM batteries (brand new, 8 years out of the last batch). 20% of that is 120 Amps. We use a Magnum charger/inverter that will theoretically deliver 100 amps and a Balmar alternator that will do the same (although we can only run it at 75% or it will overheat). We can combine solar and charger at the dock and achieve 120 amps, but eventually this will overheat the batteries and the charger will shut down. For most boats, delivering 20% of bank capacity cannot be achieved for a battery bank larger than 500 amps, and even then doing so puts a 100 amp shore power charger at maximum capacity.

Am I missing something?

Posted by: Pelican5077 | August 16, 2018 10:36 PM    Report this comment

Come on PS, the least you can do is provide a link to Rod's new website, much nicer than his old one and easier to navigate. MarineHowTo.com

After reading this, I'm convinced I made the right decision to stay Old School with FLA golf cart batteries.

Thanks for the update.

Posted by: DGL | August 16, 2018 4:09 PM    Report this comment

BatteryMinder makes a pulsing charger that is supposed to desulfate AGM batteries. I have been using it on three of my Optima Series 31s that due to mishaps when I was not aboard, have been flattened several times. These batteries are now in their 11th year. I am going to replace them with FireFlys.

Posted by: George DuBose | August 16, 2018 2:26 PM    Report this comment

Well said. I would add, don't even think of using an AGM (or Gel) battery without a Balmar or other smart regulator installed on your boat. If you are not able to install an AGM battery for this reason, the best choice among wet batteries is a golf cart style battery. If you have the room to install these batteries (taller than normal and used in pairs to get 12v) they take the abuse of a simple charging system and they charge/discharge more quickly than standard wet cell batteries.

Posted by: Dan C | August 16, 2018 1:34 PM    Report this comment

Lets not forget installing a top grade voltage and amp meter. Watching it carefully. Savvy folks buy commercial grade lead and acid with individual cells that can be measured. So when a cell fails it can be noticed and replaced. Savvy mariners running engines watch oil, temperature, voltage and amps. Batteries like humans usually die slowly. So its not too difficult to know their "health". Monthly checks with a meter on the battery terminals and distilled water top offs will keep the batteries humming for a long time.

Another thought. With batteries bigger is usually better. For boats that means 8-D's. It's the commercial standard and are readily available everywhere trucks roam. Batteries sold in Marine stores are done to a different "standard". Really good batteries have dependable handles/slings so they can be lifted. And lets not forget having a good solid f/g cover over each battery. Shorting a large battery has and can sink the boat. And send its owner to meet St. Peter.

Here's a tips about battery cables. Use 1/0 and 2/0 welding cable with neoprene jackets and both solder/crimp the ends. Will last forever. It's the stuff used by mining companies.
Welding cable with neoprene jackets is completely waterproof. The plastic insulated stuff is used only because its cheap. Boat builders always undersize battery cables to save money.

A good way to learn about batteries and their proper installation is to inspect a registered offshore fish boat or USCG patrol boat. Even megayachts typically have shabby battery installations. If the battery installation is done right the batteries ought remain in place when the boat turns turtle or lays down on its side. The damage loose batteries can do from a knockdown is awesome. Many is the boat that has been knocked down whose batteries come loose and there goes the engine when its needed.

PIBerman Norwalk CT
author: "Outfitting the Offshore Cruising Sailboat" Paracay Publ.

Posted by: Piberman | August 16, 2018 10:56 AM    Report this comment

Commercial fish boats round the boat continue to use heavy duty lead and acid batteries that with reasonable care will last a decade or more and can economically be rebuilt. When buying batteries remember lead is the expensive ingredient. Heavier the better. So buy from truck dealers. Their customers demand the best.

Bringing batteries down to 50% shortens their life noticeably. Lead acid love distilled water topped up monthly depending on use. And remember a loose battery has sunk more than one vessel.

Lead acid batteries can be economically rebuilt most everyplace in the world. Fancy stuff usually gets dumped somewhere.

Posted by: Piberman | August 16, 2018 10:00 AM    Report this comment

A side note regarding battery enemy no. 1 - the dreaded sulfiting.

Some years ago, a japanese manufacturer - Nanotech (now out of business) - devoloped a small device called a Nanopulsar the size of a deck of cards and at a cost of $150.
We bought a couple and installed them on our 4 Lifeline AGM D-4 batteries.
That was back in 2003.
All 4 batteries are still accepting a full charge and "still going strong" after more than 13 years of service, including several complete discharges due to electrical mishaps.
Too bad that these small devices are no longer available - perhaps a devious battery manufacturer bought the company :-)

Posted by: CVJ | June 10, 2016 1:27 PM    Report this comment

A side note regarding battery enemy no. 1 - the dreaded sulfiting.

Some years ago, a japanese manufacturer - Nanotech (now out of business) - devoloped a small device called a Nanopulsar the size of a deck of cards and at a cost of $150.
We bought a couple and installed them on our 4 Lifeline AGM D-4 batteries.
That was back in 2003.
All 4 batteries are still accepting a full charge and "still going strong" after more than 13 years of service, including several complete discharges due to electrical mishaps.
Too bad that these small devices are no longer available - perhaps a devious battery manufacturer bought the company :-)

Posted by: CVJ | June 10, 2016 1:26 PM    Report this comment

A side note regarding battery enemy no. 1 - the dreaded sulfiting.

Some years ago, a japanese manufacturer - Nanotech (now out of business) - devoloped a small device called a Nanopulsar the size of a deck of cards and at a cost of $150.
We bought a couple and installed them on our 4 Lifeline AGM D-4 batteries.
That was back in 2003.
All 4 batteries are still accepting a full charge and "still going strong" after more than 13 years of service, including several complete discharges due to electrical mishaps.
Too bad that these small devices are no longer available - perhaps a devious battery manufacturer bought the company :-)

Posted by: CVJ | June 10, 2016 1:26 PM    Report this comment

Yes, we are testing the Firefly, and so far its performance has been impressive.

Posted by: Darrell | March 23, 2015 4:11 AM    Report this comment

This is a great article, I especially appreciate that you jump straight to the best practices and advice bullets. I invested a lot of money into my AGM banks, and I really don't know how to keep them performing at optimum levels. I look forward to a smart charger test coming soon, I hope.

Any chance of rigging a smart battery monitoring system with Arduino or Raspberry Pi? I've been toying with the idea of constructing a shore power smart monitoring system, but it will take a while for me to reach the education levels to do so...

I wish you fair winds and following seas,

Woody Fairley

Posted by: Capt. Woody | March 21, 2015 7:35 PM    Report this comment

are you testing a fireflyinternationale bat.

Posted by: Unknown | March 18, 2015 3:52 PM    Report this comment

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