AGM Battery Failure - Two Sets in Two Years

[Pete7]

Originally Posted by rslifkin

Feeding to house first, then ACR to start is a fine way to do it, but I did it the other way for 2 reasons. It was less wiring to change on my setup, and being a powerboat, I consider starting power safety critical.

We have a similar set up but with a single sense VSR wired engine battery > house bank during alternator charging. Solar goes directly to the house bank and can't charge the engine battery (single sense VSR) I don't need it to. A second BEP switch will join the banks in an emergency though.

Pete

[BocaIII]

AGM’s charged properly will last a very long time
you have a charging issue.
Jack
W4GRJ

[argonauta1]

My thought would be to switch out of AGMs to either Gel or Conventionel flooded lead acid. I tried two 225 Amp hr AGMs and found they were simply too sensitive/vulnerable to either depletion below 70% or or incremental over charging. I switched back to Gels but eventually switched to 4 x 6V golf carts which when rigged to put out 12 V gave 440 Amp Hrs. They turned out to be bullet proof.

[SV__Grace]

We have a similar Mastervolt setup installed 2017 during an extensive refit and had the same low voltage problem after 18 months of use.

Testing- a lot of tests are reported by OP but the one that seems to be missing (or I can't find it) is to disconnect the batteries, let them sit a few hours, and test their voltage. A bad battery in a bank will have different (typically lower) voltage than the others.

This is what happened to our 1200 amp bank of 6 Mastervolt 6V AGMs. One of the batteries seemed to be dragging down the whole bank.

Since we can't just replace one bad battery and we were (and still are) out cruising and not able or willing to replace the whole bank yet, we disconnected the pair with the bad battery, going from 1200amh to 800amh, which is fine for us, and has been working fine since.

My best guess as to why is that we were loathe to follow the recommendation of our electrician who said that while cruising we should run the generator to charge the batteries to 100% at least once per week, which takes @8 hours of generator noise intruding on our peace and quiet. He calls this "balancing" the batteries. While the Mastervolt AGMs don't need to be equalized, apparently they need to be "balanced." PotAtoe, poTAHtoe to me.

We weren't doing that before, and since we've started doing that, we haven't had a problem. Typically takes 6 hours of generator time to reach 100%.

When you think about it, it makes sense that using solar and wind, and even engine power to constantly put energy into the batteries to partial SOC without regularly achieving full SOC might mess up their chemistry (note the high brow industry jargon).

Since we started "balancing" our AGMs once per week I notice a pattern that they recharge more efficiently for a day or two afterwards, then resistance builds and it takes longer and longer to bring up the SOC on solar and wind. (Hey, got nothing better to do while on the hook than monitor my batteries).

Lesson learned. We now put up with running the genny 6 hours once per week while on the hook and this winter will replace with lithium.

[mcon12000]

Originally Posted by SV__Grace

We have a similar Mastervolt setup installed 2017 during an extensive refit and had the same low voltage problem after 18 months of use.

Testing- a lot of tests are reported by OP but the one that seems to be missing (or I can't find it) is to disconnect the batteries, let them sit a few hours, and test their voltage. A bad battery in a bank will have different (typically lower) voltage than the others.

This is what happened to our 1200 amp bank of 6 Mastervolt 6V AGMs. One of the batteries seemed to be dragging down the whole bank.

Since we can't just replace one bad battery and we were (and still are) out cruising and not able or willing to replace the whole bank yet, we disconnected the pair with the bad battery, going from 1200amh to 800amh, which is fine for us, and has been working fine since.

My best guess as to why is that we were loathe to follow the recommendation of our electrician who said that while cruising we should run the generator to charge the batteries to 100% at least once per week, which takes @8 hours of generator noise intruding on our peace and quiet. He calls this "balancing" the batteries. While the Mastervolt AGMs don't need to be equalized, apparently they need to be "balanced." PotAtoe, poTAHtoe to me.

We weren't doing that before, and since we've started doing that, we haven't had a problem. Typically takes 6 hours of generator time to reach 100%.

When you think about it, it makes sense that using solar and wind, and even engine power to constantly put energy into the batteries to partial SOC without regularly achieving full SOC might mess up their chemistry (note the high brow industry jargon).

Since we started "balancing" our AGMs once per week I notice a pattern that they recharge more efficiently for a day or two afterwards, then resistance builds and it takes longer and longer to bring up the SOC on solar and wind. (Hey, got nothing better to do while on the hook than monitor my batteries).

Lesson learned. We now put up with running the genny 6 hours once per week while on the hook and this winter will replace with lithium.

The quote above is your answer..

Since you are able to monitor the loads on the system everything points to undercharging. Also the above suggestion to disconnect the batteries in question and allow them to rest for 24hrs is a great way to know the actual SOC.

[flyingfin]

Originally Posted by BocaIII

AGM’s charged properly will last a very long time
you have a charging issue.
Jack
W4GRJ

Thats only half the story - AGM's not drawn down significantly on a daily basis will last a very long time. They are best used for standby power, and then for brief period of drawdown. Suggest you switch to deep cycle marine or golf cart batteries.

[Ken Pole]

With reference to AGMS being irrecoverable below 60% state of charge, I should note that I ran down both of my FullRiver AGMs (my fault) to virtually zero. The one I used for my starter battery was toast but my battery supplier brought the House battery back to life and it continues to work fine. I continue to use it as a starter but have gone to a pair of Oasis Firefly carbon foam AGMs for the House.

[Bycrick]

Thread drift, again. The thread got dragged off about whether or not it was possible to overcharge batteries even at the "proper" voltage. Eventually it came down to "Sure. But your supposed to monitor this or that." Or "I turn something off before that happens."

I’d have left it there until I read a thread about the problems caused in some boats with bolted-on keels when they were unfortunate enough to run into something solid. One of the posts sort-of-said, "It’s not the fault of bad design, you shouldn’t have been dumb enough to run into something."

Which brought to mind the following story.




It seems that a man had gone to Levine to have a suit made cheaply, but when the suit was finished and he went to try it on, it didn't fit him at all. ``Look,'' he said, ``the jacket is much too big in back.''
``No problem,'' replied Levine, showing him how to hunch over his back to take up the slack in the jacket.
``But then what about the right arm? It's three inches too long.''
``No problem,'' Levine repeated, demonstrating how, by leaning to one side and stretching out his right arm, the sleeve could be made to fit.
``And what about these pants? The left leg is too short.''
``No problem,'' said Levine for the third time, and proceeded to teach him how to pull up his leg at the hip so that, though he limped badly, the suit appeared to fit.
Having no more complaints, the man set off hobbling down the street, feeling slightly duped by Levine. Before he went two blocks, he was stopped by a stranger who said, ``I beg your pardon, but is that a new suit you're wearing?''
The man was a little pleased that someone had noticed his suit, so he took no offense. ``Yes it is,'' he replied. ``Why do you ask?''
``Well, I'm in the market for a new suit myself. Who's your tailor?''
``It's Levine---right down the street.''
``Well, thanks very much,'' said the stranger, hurrying off. ``I do believe I'll go to Levine for my suit. Why, he must be a genius to fit a cripple like you!''

[The Sun King]

I am presently evaluating AGM batteries on my home system for use in powering my next solar boat. Better to screw up in the backyard than a thousand miles from home. For study, I acquired 3 48v strings of AGMs that had failed in 2 years. It turned out with that set that they had been grossly over charged, with up to 10kw input. AGM batteries are fussy about charge current. They have to be charged at a much lower rate than open batteries or the pressure will build and they will vent. They dry out and fail. Often, though, they can be easily restored to service.


The data sheet for the 850ah stack that I am presently testing stresses maintaining a finely regulated float voltage. That's all well and good for standby, but pretty much useless for a live system with constant input and output. Setting the charge for, say, 54.4 volts on the 48v system results in batteries that won't do very much before running down. Buried in the fine print is the admonition that every now and then they have to be bulked up to the neighborhood of 58v. The various charge controllers that I use have some program capability, but not the fine tuning of some of the controllers mentioned here by other users. Setting some of the charge controllers a little higher, the batteries can get a period of 58+ on a sunny day, and they seem happy with that.



I can say that I am quite convinced that a large standard alternator could both exceed the charging rate for a small bank and never get the top end right. I urge anyone with agm batteries to acquire and thoroughly read the data sheet. Then make sure everything that will contribute to charging is in spec.



In a dynamic system it is very nearly impossible to set up a perfect charge routine with generators, alternators, solar panels and shore power. I have mine cycling good levels of power, now. Time will tell if I am harming them. There are a good many of them and, new, they are about $1200 EACH, so I really, really don't want to harm them.


If someone comes up with an alternator with external regulator that can be set for various battery types they will have a heckuva product for the marine and RV market. The standard automotive alternator is the worst thing that ever happened to batteries.

[sailjumanji]

The first thing we did before doing any of the more extensive testing, was to charge both batteries on shore power (MassCombi), and then disconnect them and allow voltage to stabilize. This is pretty standard test for cell failure. There was no cell failure. Here is a plot for the house batteries. They stabilized at 12.96 and 12.95 volts, respectively. Voltage was stable after about 16 hrs, but still holding after 4 days.

The start battery performed similar.

[sailjumanji]

Originally Posted by Ken Pole

With reference to AGMS being irrecoverable below 60% state of charge, I should note that I ran down both of my FullRiver AGMs (my fault) to virtually zero. The one I used for my starter battery was toast but my battery supplier brought the House battery back to life and it continues to work fine. I continue to use it as a starter but have gone to a pair of Oasis Firefly carbon foam AGMs for the House.

Also, if you do a capacity test on an AGM, it is essentially running it down to "zero" (10.8 volts). I think MaineSails' - and the Mastervolt procedure - said to quickly get them back up to full charge. If that killed a battery, I don't think either of them would be recommending.

[sailjumanji]

Originally Posted by mcon12000

The quote above is your answer..

Since you are able to monitor the loads on the system everything points to undercharging. Also the above suggestion to disconnect the batteries in question and allow them to rest for 24hrs is a great way to know the actual SOC.

SOC for the two failed house batteries is 100%. And if disconnected - as per the graph I showed - they both stabilize at 12.95 volts. However, both have lost 90% of their capacity, as capacity tests showed ~20 and 30 amp-hours remaining for each. They look great on charged specs, but just have no depth. All show, no go!

[Bycrick]

Sailjumanji — You have again proved a frequently ignored point:SOC, and it’s proxy rest voltage, saysnothing about the capacity of the battery. A size-D lead-acid battery will show the same voltage as an 8-D lead-acid battery.

[sailjumanji]

Originally Posted by flyingfin

Thats only half the story - AGM's not drawn down significantly on a daily basis will last a very long time. They are best used for standby power, and then for brief period of drawdown. Suggest you switch to deep cycle marine or golf cart batteries.

I'm still on warranty batteries, so no need to make that change now. I think Mastervolt considers these high-capacity AGM's to be deep cycle. Also, our overnight usage hasn't exceeded 25% of original capacity (80-100 AH out of 450 AH original capacity), and we've just upsized to 540 AH capacity. If we get the system correct, the next time these batteries need to be changed out, will probably go lithium. But I have hope for these AGM's. We don't abuse them, and are constantly watching to make sure we don't deep discharge. The AGM's on our last cat lasted over 10 years, on a similar solar and shore power setup.

Right now one strong explanation is that the solar charger appears to be sensing full battery sooner than reality, and going to float. And that after several days of this, we are running deeper discharge than shown on AH counter. It's a bit tough to see it in the voltage because there is always a load. The other side of the puzzle though is that this last set of batteries failed on shore power. And so far, that system has worked to spec on every test we have run.

[CarlF]

My understanding is that most AGM’s don’t mind a long absorption (e.g, at 14.4v). If it’s OK with MasterVolt, I would just increase the minimum absorption time on your solar controller to 4 or even 6 hours.