Why are so many in Love with AGM's

[waterman46]

I only use AGM's on my boat. They are completely sealed, so I don't ever worry about adding water or having to deal with spilled acid.Flooded cells are less expensive of course, and just fine if you have the time and inclination to check them every so often, and that means you also should probably not leave them unattended for months at a time. That won't work for me since I leave the boat unattended for the entire hurricane season.

[Cabo Jim]

Originally Posted by flyingfin

I have had nothing but problems with AGM batteries, from early failure after 18 months in lawn equipment, failure after 24 months in road vehicles (seems the batteries have insider knowledge of the warranty expiration date), to full blown melt-down and fire at cell tower standy power cabinets. Never had theses issues with lead-acid batteries. Is it because the AGM's are sealed and cannot gas-off?

Speaking of thermal runaways with AGM batteries. I had a house bank of 5 Deka group 31 AGM batteries that were about 5 years old and while I was plugged in to a 30 amp service, we experienced a thermal runway. My wife was cleaning and called me to "come quick" I dropped what I was doing and came below and could smell sulphur. I opened the battery cabinet and released a cloud of steam. I could not touch the batteries they were so hot. I didn't bother to check the charger to see what it was putting out. I just shut it down. AGM batteries do have the capability to off-gas.
I believe there was an internal short in one of the batteries. HOLY S_ _T THELMA!!! that was way too close. I replaced them with conventional lead acid batteries but after 3 years I switched back to a higher quality Life Line AGM battery bank after a successful series of visits to my therapist.

[sailinglegend]

Originally Posted by mitiempo

....Scrolling to the end 5 hrs and 42 minutes with a 20 amp charger and 5 hrs and 30 minutes a 40 amp charger. 105 AH battery
https://marinehowto.com/how-fast-can...ry-be-charged/
...

Misquoting Mainesail's very long and very often misquoted article only confuses this thread even more.

As much as I respect all his work in this case he didn't use a 40 amp "charger" but a 40 amp "charging source" which didn't drop to float mode when it "thought" the battery was full. So the time quoted to actually get to 100% charge is meaningless.

Repeating the test with an FLA battery and comparing the results would be more interesting.

[mitiempo]

Originally Posted by sailinglegend

Misquoting Mainesail's very long and very often misquoted article only confuses this thread even more.

As much as I respect all his work in this case he didn't use a 40 amp "charger" but a 40 amp "charging source" which didn't drop to float mode when it "thought" the battery was full. So the time quoted to actually get to 100% charge is meaningless.

Repeating the test with an FLA battery and comparing the results would be more interesting.

A properly programmed charger be in constant current mode (bulk) until absorption is reached. It then maintains the absorption voltage until the battery is accepting very little current. It then goes to float - where the battery really doesn't appreciably charge. A charger should not go into float until the battery is about 99% SOC.

So I do think the test was valid.

[mjgill1]

Originally Posted by mitiempo

Fast charging of Agm batteries is nowhere near as fast as some might think. From 50% SOC to 85% SOC is quicker but 85% to 100% takes just as long as Fla batteries. Here's an interesting link showing the results. Scrolling to the end 5 hrs and 42 minutes with a 20 amp charger and 5 hrs and 30 minutes a 40 amp charger. 105 AH battery
https://marinehowto.com/how-fast-can...ry-be-charged/

Gel batteries can be a very long lasting battery if treated properly. 15 years is not uncommon.

Wow! That was one heck of an article. Thanks for the education. It sure puts a lot of things to rest...
What do you think of this charger? It's what we got a few years ago when out other one crapped out. We have a house bank of 2 110ah agm and a single 110ah agm start battery. Can't recall the brand off hand. I programmed the charger according to the instructions. Should we depart from that and go to a custom program? IF so, what do you suggest? https://www.promariner.com/en/63130

[sailinglegend]

Originally Posted by mitiempo

....A charger should not go into float until the battery is about 99% SOC.

This is the ideal world but many 'smart' chargers are not that smart and drop down to 'float' much too early. They are designed to charge the battery - not overcharge it", so at float they may only be 90% charged or less.

This is confirmed in another long article by Mainesail @ https://marinehowto.com/installing-a...ttery-charger/

I quote a section:

In an ideal recharge a battery charger would not drop to float voltage until the battery bank had attained the 99.5% to 100% SOC point. Almost all battery chargers out there, for marine use, drop to float before the battery bank has attained 100% SOC. While this makes them “safe“, for the manufacturers lawyers, it also means that in order to get back to 100% SOC it just takes a bit longer. At a dock this is not a huge deal, if we are getting into the mid to upper 90’s before the float transition. Once the charger drops to float this dramatically extends the time it takes to get to 100% SOC. The absorption cycle is perhaps the most important stage of charging and if it is too short, due to an egg-timer, the batteries can become chronically under charged and suffer the effects of sulfation.

Unfortunately far too many chargers out there work on the simple “egg-timer” principal. Here’s how an egg-timer charger usually works.

Battery Charges In Bulk Stage Increasing Bank Voltage
Battery Bank Attains Absorption Voltage Limit
Once Absorption Voltage Limit is Attained a Fixed Timer Starts
When Egg-Timer Ends the Charger Drops to Float
Hmm??

As a Marine Service provider I would have expected you to know all this.

[Pete7]

Originally Posted by Simi 60

So that's a no then, no real life lp4 longevity examples only theory on paper

But what is a battery cycle


So how does that work for us when out bank never gets below 80% so apparently, never sees a cycle?

There is a YT vlog of a RV couple living full time on board who trashed a set of LFP batteries at the 8 year point by mistake. They put the van in storage inside so no solar and didn't disconnect the battery completely. The BMS took some power as did the LED on each cell. 8 months later the bank was toast and they were crying in their soup. However, 8 years of living off a LFP bank sounds pretty good to me.

I was reading last night that Trojan in the brochure say that a cycle is down to 80% and back to full charge straight away for their deep cycle FLA batteries. That's perhaps why some of their graphs show 600 cycles but doesn't mention at 70% whilst other graphs show 1500 at 50%.

Pete

[mitiempo]

Originally Posted by Pete7

There is a YT vlog of a RV couple living full time on board who trashed a set of LFP batteries at the 8 year point by mistake. They put the van in storage inside so no solar and didn't disconnect the battery completely. The BMS took some power as did the LED on each cell. 8 months later the bank was toast and they were crying in their soup. However, 8 years of living off a LFP bank sounds pretty good to me.
-------------------------------------------------------

8 years should be easily attainable with Fla GC batteries

-------------------------------------------------------

I was reading last night that Trojan in the brochure say that a cycle is down to 80% and back to full charge straight away for their deep cycle FLA batteries. That's perhaps why some of their graphs show 600 cycles but doesn't mention at 70% whilst other graphs show 1500 at 50%.

Pete

A cycle is whatever it is quoted as. Trojan batteries are quoted at 50% SOC.

[mitiempo]

Originally Posted by sailinglegend

This is the ideal world but many 'smart' chargers are not that smart and drop down to 'float' much too early. They are designed to charge the battery - not overcharge it", so at float they may only be 90% charged or less.

This is confirmed in another long article by Mainesail @ https://marinehowto.com/installing-a...ttery-charger/

I quote a section:

In an ideal recharge a battery charger would not drop to float voltage until the battery bank had attained the 99.5% to 100% SOC point. Almost all battery chargers out there, for marine use, drop to float before the battery bank has attained 100% SOC. While this makes them “safe“, for the manufacturers lawyers, it also means that in order to get back to 100% SOC it just takes a bit longer. At a dock this is not a huge deal, if we are getting into the mid to upper 90’s before the float transition. Once the charger drops to float this dramatically extends the time it takes to get to 100% SOC. The absorption cycle is perhaps the most important stage of charging and if it is too short, due to an egg-timer, the batteries can become chronically under charged and suffer the effects of sulfation.

Unfortunately far too many chargers out there work on the simple “egg-timer” principal. Here’s how an egg-timer charger usually works.

Battery Charges In Bulk Stage Increasing Bank Voltage
Battery Bank Attains Absorption Voltage Limit
Once Absorption Voltage Limit is Attained a Fixed Timer Starts
When Egg-Timer Ends the Charger Drops to Float
Hmm??

As a Marine Service provider I would have expected you to know all this.

Yes, I know this of course. But is a charger goes to float at 90% SOC you can add hours to charge time. The test showed ideal conditions. My point being Agm batteries are not that fast to a full charge. With float being entered at 90% SOC that could easily make charging time 8+ hours.

At the correct voltage for a given battery not going into float before 99% SOC will not overcharge a battery.

[mitiempo]

Originally Posted by mjgill1

Wow! That was one heck of an article. Thanks for the education. It sure puts a lot of things to rest...
What do you think of this charger? It's what we got a few years ago when out other one crapped out. We have a house bank of 2 110ah agm and a single 110ah agm start battery. Can't recall the brand off hand. I programmed the charger according to the instructions. Should we depart from that and go to a custom program? IF so, what do you suggest? https://www.promariner.com/en/63130

The PronauticP has 2 sets of settings. Just make sure that the voltages agree with your battery manufacturer's recommendations for charging voltages.

Remember to use the supplied temp sensor.

It is a very good charger.

[sailinglegend]

Originally Posted by mitiempo

....My point being Agm batteries are not that fast to a full charge. With float being entered at 90% SOC that could easily make charging time 8+ hours...

None of that opinion came from Mainesail's post - which is even more confusing each time I read it.

He shows this diagram of the 0.2C and 0.4C charging rates which show getting to Absorption about 4 times faster at 0.4C.

Mainsail graph 0.2C and 0.4C.jpg Views: 87 Size: 304.7 KB ID: 233240" style="margin: 2px" />

He then says:

50% SOC @ .4C For 1 Hour = 85% SOC – Exited Bulk @ 19 Minutes

50% SOC @ .2C For 2 Hours = 87% SOC – Exited Bulk @ 1:16

That means the change from Bulk to Absportption is not happing at the same SoC. It also means gettings to 85% SoC at a low 0.2C charge rate is about twice as slow as charging at 0.4C?????

FLAs would be at about 0.1C - so the difference compared with AGMs at a high charge rate is even more dramatic.

So in the real world when the charge current starts to fall it would make sense to stop the genset or engine running sometime after the Absorption stage has started, and then let the solar take over. That would happen about 4 times faster at 0.4C as against 0.2C. FLAs may be charged at 0.1C so the bottom line is AGMs can get to absorption much faster than FLAs.

I'm not saying they can fully charge a bank 4 times faster - I'm just interpreting Mainesail's findings. Lifeline AGMs say they can charge 20% faster than FLAs and I would agree with that. Any saving on genset or engines use surely has to be worth it?

[Simi 60]

Originally Posted by Westcliffe01

Tesla battery modules
22V Nominal, 5.2kWh
27x12x3" in size
58lb per module
cost each $1390 + shipping

Of interest, this from the Lithium batteries on a boat FB page

There seems to be a lot of interest by people looking to purchase a used Tesla battery pack for a marine application.
There is the "Cool" factor
Tesla's battery design is one of the best in the automotive market
The pricing seems reasonable.
​They are more efficient than LiFePo4 chemistries​
BUT we did some research on them and decided against it for the following reasons:
Tesla packs use a Lithium Colbalt chemistry which is more susceptible to thermal runaway
They also require a class D fire extinguisher
If put under moderate loads they require a liquid cooling system
Their ou​t​put is 18-24 volts which is too low for 24V system​s​ which typically operate at 24-28 volts, so inverters will trip and other devices will run at higher currents causing premature failure.
​Their output is too high for 12V systems which typically work at 12-14 volts.​
They have special BMS requirements and are far from plug and play
In conclusion folks, play it safe and use LiFePo4 cells in your non-commercial marine applications.
Disagree? We would love to hear how you are overcoming these issues in your marine application
A bit more on the Tesla battery BMS
The Tesla Model S Battery Module has it's own proprietary Battery Management System board that reports the voltage of each cell in the module, temperature of each module terminal, and can actively balance each cell in the module. But it uses a very proprietary serial communications scheme to report this to the main BMS board in the Tesla Battery Pack.

https://www.facebook.com/groups/427372107686109

[mitiempo]

Originally Posted by sailinglegend

None of that opinion came from Mainesail's post - which is even more confusing each time I read it.

He shows this diagram of the 0.2C and 0.4C charging rates which show getting to Absorption about 4 times faster at 0.4C.

Attachment 233240

He then says:

50% SOC @ .4C For 1 Hour = 85% SOC – Exited Bulk @ 19 Minutes

50% SOC @ .2C For 2 Hours = 87% SOC – Exited Bulk @ 1:16

That means the change from Bulk to Absportption is not happing at the same SoC. It also means gettings to 85% SoC at a low 0.2C charge rate is about twice as slow as charging at 0.4C?????

FLAs would be at about 0.1C - so the difference compared with AGMs at a high charge rate is even more dramatic.

So in the real world when the charge current starts to fall it would make sense to stop the genset or engine running sometime after the Absorption stage has started, and then let the solar take over. That would happen about 4 times faster at 0.4C as against 0.2C. FLAs may be charged at 0.1C so the bottom line is AGMs can get to absorption much faster than FLAs.

I'm not saying they can fully charge a bank 4 times faster - I'm just interpreting Mainesail's findings. Lifeline AGMs say they can charge 20% faster than FLAs and I would agree with that. Any saving on genset or engines use surely has to be worth it?

True, the larger the charge source for a given bank size the quicker to absorption voltage. If a bank is charged with a very low output source, say a smallish solar array with a large battery bank, the absorption voltage is often not reached until the bank is at or higher than 90% SOC.

[timb7734]

In addition, “new” AGMs should be checked for manufacture date prior to purchase from supplier, this date is embedded in the serial number. These batteries need a monthly charge at the warehouse or distributor and if they are not they come to you as prematurely aged and the battery life shortened. If the supplier is not charging monthly then take the freshest batteries (newest by date of manufacture) in the inventory, preferably thirty days or less.

[Dockhead]

Originally Posted by sailorboy1

People like AGMs when they accept the marketing hype and luck out as it having worked out for them. To my mind their only advantages are you don't have to water them and they don't spill. Everything else is just marketing hype!

Even if that is true, those advantages you state are very important, even critical, for some people.


I use Trojan T105's in my present boat, but we could only use AGMs in the previous boat because the only space for batteries was not accessible in a way which allow you to water or maintain FLA's there. We had no choice.