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Batteries losing 20% capacity permanently with each discharge cycle

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  • #16
    I managed to open the batteries and check the fluid level. It seems that wasn't the problem after all. All plates were covered by the electrolyte. Even so, the battery voltage shows a full charge, 12.7V, but the acid density is only 1.13g/ml.

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    • #17
      Originally posted by Mikzi View Post
      At this stage the acid density for the batteries only goes from 1.10 g/ml when discharged to 1.15 g/ml at full charge, but at full charge they still show 26V, SOC 100%, while at rest.
      <snip>
      I'm at a loss for ideas on how to restore the battery capacity, or why the max capacity is diminishing so quickly. Or why the battery voltage is showing a full charge even when the acid density is so poor.
      Originally posted by Mikzi View Post
      The electrolyte level for the batteries is still good, so I don't think that is the problem.
      Originally posted by mapmaker View Post
      How do you know the electrolyte level is OK? Aren't the batteries sealed?
      Originally posted by Mikzi View Post
      These are sealed floating batteries, not gel or agm, so refilling is possible. Mapmaker was right in that despite the batteries being sealed the electrolyte had somehow escaped.
      Originally posted by Mikzi View Post
      I managed to open the batteries and check the fluid level. It seems that wasn't the problem after all. All plates were covered by the electrolyte. Even so, the battery voltage shows a full charge, 12.7V, but the acid density is only 1.13g/ml.
      Mikzi, I think there is a communication problem... we're not talking the same language. In your original post, you described your acid density as 1.10 g/ml. But you had never opened the battery to check. (btw, in a sealed battery there is usually no free liquid electrolyte to check with an hydrometer. It is sometimes possible to extract enough to test with a refractometer. I really don't know what you have for batteries. the magic eye suggests there is free liquid electrolyte).

      Then you said the electrolyte level is still good, then you said the electrolyte had escaped, and most recently you said its level was OK, but its density was not. How did you measure the density?

      You talked about testing capacity, but as Sunking pointed out your test was meaningless.

      I really don't know what advice to give... we're not speaking the same language... what you have been describing doesn't make a lot of sense to me.

      --mapmaker
      ob 3524, FM60, ePanel, 4 L16, 4 x 235 watt panels

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      • #18
        Originally posted by Mikzi View Post
        I managed to open the batteries and check the fluid level. It seems that wasn't the problem after all. All plates were covered by the electrolyte. Even so, the battery voltage shows a full charge, 12.7V, but the acid density is only 1.13g/ml.
        1.13g/ml? I am lazy today and not going to try to figure that out. How does that translate to specific gravity. Specific Gravity is what you want to know.
        MSEE, PE

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        • #19
          Thanks for the clarification, Inetdog. You're right that these are maintenance free FLA batteries with hard to open vent caps, not sealed. My mistake.

          Let me clarify, Mapmaker. The magic eye marker on one of the L36 batteries had recently turned white, which was why I believed the fluid level was low and had somehow escaped. But when I managed to get that battery opened there was no missing fluid. So the white marker must indicate something else.

          Another clarification. The L36-100 model I'm trying now have hard-to-open-vent-caps, but the L35-100 model I tried first were normal FLA batteries. I could open them to check the acid. That's how I could determine the specific gravity only went from 1.10 (no charge) to 1.15 (20%). Now with the L36 battery opened I can see that its gravity also only stays within this interval.

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          • #20
            Originally posted by Sunking View Post
            1.13g/ml? I am lazy today and not going to try to figure that out. How does that translate to specific gravity. Specific Gravity is what you want to know.
            Except for temperature compensation, the calculation is amazingly easy.
            Since water is 1g/ml, an electrolyte which measures 1.13g/ml has an SG of 1.13.
            SI units work out very well in this particular case.
            Sounds more like you are not awake yet than that you are lazy.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #21
              Originally posted by inetdog View Post
              Except for temperature compensation, the calculation is amazingly easy.
              Since water is 1g/ml, an electrolyte which measures 1.13g/ml has an SG of 1.13.
              SI units work out very well in this particular case.
              Sounds more like you are not awake yet than that you are lazy.
              You would be right, and if the SPG is 1.13 indicates roughly between 30 and 40% SOC. Not good. He is looking for something up around 1.28.
              MSEE, PE

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              • #22
                Originally posted by Sunking View Post
                You would be right, and if the SPG is 1.13 indicates roughly between 30 and 40% SOC. Not good. He is looking for something up around 1.28.
                Which leads to the question of why he is not successfully getting back to 100% SOC even after he has reached what he thinks is the proper cutoff voltage.

                1. Lack of compensation for voltage drop in the leads between the CC and the battery? Maybe the most likely.
                2. Lack of temperature compensation of charging voltages? The effect would be in the wrong direction unless the batteries were very cold.
                3. Incredibly rapid sulfation?
                4. ?
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                • #23
                  Originally posted by inetdog View Post
                  Which leads to the question of why he is not successfully getting back to 100% SOC even after he has reached what he thinks is the proper cutoff voltage.

                  1. Lack of compensation for voltage drop in the leads between the CC and the battery? Maybe the most likely.
                  2. Lack of temperature compensation of charging voltages? The effect would be in the wrong direction unless the batteries were very cold.
                  3. Incredibly rapid sulfation?
                  4. ?
                  I doubt #1 beacuse even if the wires are undersized would only slow down the process. If it reaches float and stays there a few hours current tapers down to almost nothing in any constant voltage method as the battery voltage reach full charge level. If I had to guess it would be one cell in a string gone bad in open which can only be found with a hydrometer or internal resistance test of each cell which you cannot do in a multi-cell battery like 12 volts. Sounds like warranty claim to me.
                  MSEE, PE

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                  • #24
                    Originally posted by Sunking View Post
                    I doubt #1 beacuse even if the wires are undersized would only slow down the process. If it reaches float and stays there a few hours current tapers down to almost nothing in any constant voltage method. If I had to guess it would be one cell in a string gone bad in open which can only be found with a hydrometer or internal resistance test of each cell which you cannot do in a multi-cell battery like 12 volts. Sounds like warranty claim to me.
                    Seems like it.
                    What I was thinking of for #1, possibly a bit far fetched, was that the float voltage would be reached with current still somewhere in the Absorb range and because the CC will regulate to that voltage the batteries could be steadily increasing in SOC with the voltage measured at the CC remaining stable. If the OP measures the "float" voltage with a meter at the battery terminals then that whole explanation goes out the window.
                    There is a chance that you could narrow a single cell anomaly down to one battery if you had two or more 12V batteries in series, but for a parallel arrangement you would be screwed. For parallel batteries, disconnect and run the same charging tests individually.
                    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                    • #25
                      Load Test will find it.

                      If he has a conventional charger assuming it has capacity to actually charge the battery, put it on for 24 hours. I also suspect a possibility of inaccurate hydrometer and volt meters.
                      MSEE, PE

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                      • #26
                        Thanks for all the input.

                        I'm using fairly thick 16mm^2 copper wires between all batteries and to the 24V MPPT charger, located less than a meter away. I measure the voltage at the batteries, but the charger measures it through the same wires it uses to charge, so at 20A there is a slight voltage drop (0.6V). But nothing that I think would explain this behavior.

                        Yuasa recommends 14.4V charge voltage and max 20 amp for a 200AH battery pack, so that's what I've been following. The batteries are indoors in a garage, about 20 °C.

                        I will follow Sunking's advice and try to charge a single battery for 24 hours with a conventional charger to see if that helps increase the gravity beyond 1.15.

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                        • #27
                          Mikzi sure sounds like you have an open cell. Classic symptom of a open cell or sulfated battery is low Specific Gravity, when place on charger, the charger is fooled and indicates the battery is fully charged very quickly, and the battery cannot support a load in which the voltage drops immediately.

                          If float charging does not work, then you have nothing to loose by cranking the voltage way up (16, 17, 18 volts and try to force current into it. Bu tit sure sounds like your battery is toast and time for a warranty claim.
                          MSEE, PE

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                          • #28
                            Originally posted by Mikzi View Post
                            I will follow Sunking's advice and try to charge a single battery for 24 hours with a conventional charger to see if that helps increase the gravity beyond 1.15.
                            If one battery charges properly and the other does not you will have your answer.
                            PS: The battery that does not increase in SG when charged separately is the bad one.
                            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                            • #29
                              The results are in. All four batteries are equally bad. I've tried recharging each one of them with a conventional charger, for up to 24 hours, but the gravity for none of them will rise beyond 1.15. Not even if I increase the voltage. At this stage I'm pulling the plug on their life support and declaring them dead. The mistreated five year old battery in my lawn mower is healthier than all of them put together. The MPPT charger isn't to blame either. It is able to charge and recharge car batteries without any issues.

                              I'm going to go with Inetdog's "Incredibly rapid sulfation" theory, seeing as how the batteries could in fact deliver 200AH, if one for the first cycle. Or perhaps the batteries were sulfated from the start but had gone through some procedure to revive them before being sold, with the shortcoming that their capacity would quickly deteriorate again, unbeknownst to most customers. The retailer is legit, but he may have gotten a bad pallet of batteries for some reason. I'm going to do a warranty claim and go with another brand and go for gel or AGM batteries instead.

                              Thanks for all the help.

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                              • #30
                                Gel is an all around bad idea for solar generally. Typical C/20 max current charge (slow) in bulk, and on the back end low charge acceptance rate in float. Toss in some voltage abuse and pow.

                                Even if a retailer seems legit, make sure they are in fact "authorized", meaning that genuine warantee claims are backed by the factory, and not just the retailer, who may take his gripes to some 3rd party. I've seen Optima batteries sold as new, when in fact they were just cleaned up, and cranked on with some kludge of a recondition charger. Basically they got intercepted on the way to the recycler, and pawned off on ususpecting customers or distributors.

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