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robert-4 asked

Diagnos of damaged AGM Deep Cycle batteries

I have during two year got three Victron AGM Deep Cycle, 110Ah, BAT412101084, batteries damaged. They have been connected to Ctek D250SA-Smartpass120 charging system in my boat.

The batteries have now a measured 20C to around 10Ah. The CCA i still measured to over 500A and have a internal resistance of 4mohm.

I suspect that the chargers have over charged the batteries and the electrolyte is cooked. I have a installed Victron BMV-712 that could measure at one occasion that the D250A went up in absorption mode in 3 hours. The current thorough the three batteries was below 0.5A and the voltage 14.5V. The batter was fully charged before this started.

Are there any way to determine how the batteries have been damaged?

Is there any way to diagnose the batteries so I can be sure that they are over charged and has been gassed out? I'm prepared to open the battery to make the analysis.

AGM Battery
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Mike Dorsett avatar image Mike Dorsett commented ·

If the discharge current can still hit 500A and the resistance is ~4mOhm, then it's most probable that they are sulphated, rather than boiled. Sulphation will restrict the discharge capacity, but a 'fully charged' sulphated battery can still produce the amps for a short period. Other symptoms would be a rapid rise in terminal voltage when a charger is connected - little time in bulk mode, with rapid shift to float. Also, the 14.5V would seem a little high.


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robert-4 avatar image robert-4 Mike Dorsett commented ·
The problem is that the battery voltage has never been low. I've logged the battery voltage all year round and it is always connected to solar panels.

At few occations I discharge the battery when I am in the boat.

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pwfarnell avatar image pwfarnell robert-4 commented ·
Have the batteries been overcharged and caused some other problem such as positive grid corrosion which can happen with AGM. I am not sure if this degradation would still give a high VCA and low capacity.

The charger you link to has 2 AGM settings, a 14.4V based one and a 14.7V based one. Which did you use, the Victron batteries are lower charge voltage types. Did the charger do equalisation, this should be disabled for Victron AGM. Finally, if left for long periods unused the Victron datasheet lists a storage voltage of 13.2V.

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robert-4 avatar image robert-4 pwfarnell commented ·

I have used the chargers in two different setups during my five years of use. In my first setup it was in AGM mode. In the last two year I had in the normal mode with lower absorbtion voltage.
This year I could see the voltage vs time with the BMV-712. I showed clearly that the Ctek chargers started long time absorbtion even when the service batteries were full.
See how the voltage goes up when the engine starts at 11:52 and stops at 14:26, when I arrive 2.5h later. It couldn't be healthy for the batteries.
I'have registered any equalization process.
I have a complete report if you are interested.
img-0158.png

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img-0158.png (53.0 KiB)
robert-4 avatar image robert-4 pwfarnell commented ·
I have overcharged my batteries during two setups. At my first setup I had two Victron AGM Super Cycle. There I used the 14.7V. After I discovered that they were broken with battery test instrument that could measure CCA. That occasion the CCA were low. After contact with Cetek support they recommended me to only use the AGM setting sparsely. So I mounted a switch on that setting.

Then I purchased three new Victron AGM Deep Cycle batteries and only used Victron MPPT solar regulators instead the built in regulators inte CTEK D250SA. It made it possible to log the voltage over the batteries. 2023 I installed a BMV-712. With that I could see that the service batteries was in absorption even no current was going through the batteries.

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pwfarnell avatar image pwfarnell robert-4 commented ·
Post some screenshots of your MPPT and BMV settings. I have Victron telecom batteries which are like the super cycle batteries and if these are already full, the absorption lasts only a few minutes. I use tail current to stop absorption. Is your MPPT a SmartSolar.
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robert-4 avatar image robert-4 pwfarnell commented ·

My problem is not my settings with the Victron equipment. The problem is that the Ctek D250SE doesn't stop the absorption charging even if the tail current is low. That function is not possible to adjust.


My MPPT are using the BMV-712 to detect the current through the service batteries with a wireless VE-network. It works perfect and doesn't overcharge the batteries. I will continue using that method in my future system where I will replace the Cetek equipment with a Orion XS 50A.


My main question is if it's possible to prove that a Victron battery is destroyed by overcharging. It had improved my case against Cetek when I complain about the D250SA's functionality..

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pwfarnell avatar image pwfarnell robert-4 commented ·
No idea short of cutting it open if you know what you are looking for
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robert-4 avatar image robert-4 pwfarnell commented ·
I have no problem to open it. I anyway see them as garbage. I just need some support to see know what I should look for, as you mention.
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2 Answers
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kevgermany answered ·

Given the situation, there's little to gain from opening the batteries.

Suggest you replace the ctek with a better charging system. If you can, replacing with lithium batteries would be a good move. If you're away from the boat for long periods, these can be left with charger off, unless there are other loads, like a bilge pump.

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robert-4 avatar image
robert-4 answered ·

That is a perfect solution. As a matter of fact I'm already in that process. I will convert almost all equipment to Victron.

  • Two Victron MPPT Smartsolar
  • Victron Phoenix Smart IP43 1+1 50A Charger
  • Victron Orion XS 50A DC-DC Battery Charger
  • Victron Smart Battery Sensor
  • Victron BMV-712 BMS. Overall BMS.
  • Four EVE 304 Ah LiFePo4 cells
  • JB Smart BMS 200A. Battery BMS

Just now I'm waiting for better weather to make the installation. :)

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kevgermany avatar image kevgermany ♦♦ commented ·
Sounds good. Suggest you check the info the BMS can give and if it's Victron compatible. The better BMSs will provide current and state of charge info, but not sure if that happens with what you're thinking of. @klim8skeptic might know more.


Then look at substituting an Ekrano or Cerbo plus screen for the BMV.
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robert-4 avatar image robert-4 kevgermany ♦♦ commented ·
I have made a detailed study of the manuals and it looks like I can use the BMV-712 and the Smart Battery sensor as feedback for the Orion XS and Phoenix chargers.

The JB Smart will only be used as battery protection that also has the voltage detection of each cell. I will never purposely charge to 3.65V/cell and trip the JB BMS. 3.5V will be sufficient.

The good thing with Victron is that most parameters are adjustable.

Still the JB BMS supports Victron Venus OS, via RS485, so I could integrate it with a Cerbo GX in the future. But I don't believe it will be necessary.

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klim8skeptic avatar image klim8skeptic ♦ robert-4 commented ·

@robert@hedstroms.com The JB Smart will only be used as battery protection that also has the voltage detection of each cell. I will never purposely charge to 3.65V/cell and trip the JB BMS. 3.5V will be sufficient.

Sounds like a plan, not every one needs their BMS to control solar chargers (amongst other stuff) and simply want the BMS to protect the cells.

Do charge the cells to 3.5v, then trip OVP at 3.65v / cell. You need a little bit of differential for the balancers to work. Cells do not burst into flames, or instantly degrade when they reach 3.65v.

One thing to note, most off the shelf BMS have pathetic cell balance currents. An active balancer with 4-5a would be recommended.

Skip the SBS, and if you require an additional temp sensor, buy a temp sensor for the BMV 712.

Most BMS dont have accurate current or Soc reporting. Inaccurate, offset below xx amps, or stupid rules to reset the Soc to 100%. A properly set up BMV will be better.

I missed the Smart Networking (not available at the time) and went to a GX with DVCC / SVS / STS enabled. SCS is not required, as my batts will handle any current the system will throw at them (fuses will protect the batt should any excessive currents happen). The only thing I cant remotely monitor via the GX is the cell voltage.

Blue skies.

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