What causes positive plate growth?

keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭

Can someone explain to me what causes positive plate growth in a battery?

What is happening to the positive plate to cause it to grow?

I have a set of 16 Group 3 size 105AH Concorde Lifelife AGM batteries that I bought new last year. They were new but old stock that sat for a while in a factory that used them in the production of one of their products. They sat idle for some years. When I got them last year, they were all still in their carboard factory packaging. When I checked SOC voltage on them, they were all around 50% SOC. Obviously that is not good and they sat for a long time. I knew I was taking a chance, but I got them for 1/4 normal price, so I decided to give them a try.

Anyway, I notice that the battery cases around the positive posts are bulging slightly higher. This is true on most (if not all) of them. It's not severe, but I can notice a slight difference. It's slight enough that I don't think it'd even show up in a noticeable way on a picture, but in any case I can notice this. If I hadn't read about positive plate growth in the recent past, then I would not even have noticed this. In fact, I'm pretty sure that they were like this when I got them last year, but I didn't even notice because it was so slight. That's why I wonder what causes positive plate growth. I wonder if just sitting in a discharged state for a long time (prior to my buying them) would cause this.

Just wondering what causes it so that now I can be extra careful to avoid any further unnecessary positive plate growth. I realize that too much of it will mean the death of a battery.



  • BB.BB. Super Moderators, Administrators Posts: 30,485 admin
    Re: What causes positive plate growth?

    How often/how hard do you equalize the batteries? (thinking possible corrosion from oxygen formed during equalization at the positive plate).


    PS: Is the side of the case beginning to bulge?
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What causes positive plate growth?

    normally these don't get eq'ed being agms even though concorde now states they can be. if that is done it should be as per their instructions and not very often. you need to make sure to charge all of the batteries as equally as possible making sure wires and their resistances are the same for all of the batteries
    i have noticed one corner of mine had lifted slightly also and i contacted concorde on it. they said everything is fine with it doing that and there's nothing to worry about. it does make me wonder as it doesn't seem normal, but they said otherwise. i do not have anything showing on my + post, but a small amount showed up on my - post that i just cleaned away.
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: What causes positive plate growth?

    Because these sat for so long and don't get up to 100% SOC voltages after a full charge (more like 80%), I once "equalized" them at 14.4V for 8 hours. I could not get myself to cook them at 15.5V. I know that's what Concorde suggests, but I have not had the courage to do so yet at such high voltges on a sealed battery.

    Out of the 16 batteries, I had a slight trace of white around one negative post. The seal around that post must not have been perfect. It was only a tiny bit. I cleaned and sanded around that post and poured epoxy to seal that back up. I also noticed 1 positive post that also has a small bit of white around the outer ring of the epoxy seal area. That battery in the bank is not easily accessible, so I'd have to take apart my whole battery bank to get to it to try to seal it.

    Sides of the battery are not bulging. Only the top corner near the positive post seems to be slightly higher. It's very slight, but noticeable if I look carefully. Just as a precaution, I am thinking of taking my whole battery bank apart and cleaning/sanding around each post and encapsulating that area in epoxy. The idea of a sealed AGM battery venting at all (even very slightly) concerns me since there is no way to replenish the lost water.

    I've got 4 sets of 4 batteries set up in my 48V bank. The 4 batteries in each set are interconnected with 1" x 1/8" thick copper bar. I then use 4/0 cable to interconnect between all 4 sets. I even cross connected the 4 sets "redundantly" with 4/0 just to make sure there was very little resistance between the sets of batteries.

  • BB.BB. Super Moderators, Administrators Posts: 30,485 admin
    Re: What causes positive plate growth?

    I had forgotten that about Concorde Lifeline AGM batteries:
    WARNING: This procedure should only be done in a well ventilated area because a significant amount of hydrogen gases may be released from the battery.

    1. Stabilize the battery at 68-86°F (20-30°C) for at least 24 hours prior to testing.
    2. Charge at a constant current of 5% of rated (20 hour) capacity until the voltage reaches 15.6 volts (7.8 volts for a 6 volt battery), then continue charging at this rate for an additional 4 hours. Note that the charging voltage may get as high as 18.0 volts (9.0volts for a 6 volt battery), so the power supply must be capable of outputting this level to maintain constant current. This constant current charge may take 16 to 20 hours.

    CAUTION: If the battery becomes hot (above 130°F/55°C) during this charge, stop the current and allow the battery to cool to room temperature before continuing the charge.

    3. Perform a capacity test as described in Section 5.7.
    4. If the capacity is less than 80% of the battery’s rating, steps 2-3 may be repeated up to 2 times. Be sure to start the constant current charge with a fully discharged battery.

    NOTE: The above procedure should be performed by an experienced battery maintenance facility utilizing the proper charging and test equipment. Concorde recommends the use of our Model CA1550 charger/analyzer. For more information regarding Concorde’s test equipment go to: www.concordebattery.com/accessories.php.
    I agree--that sounds like something that would cause more harm than good... But I am not a battery engineer.

    And for the other thread "where does the 5% rate of charge rule of thumb come from"--Here is another example.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: What causes positive plate growth?

    Looking at that link in Bill's post - they have a special charger that has adjustable constant potential (voltage) or constant current and has a timer.

    Seems to me, if I were going to attempt that procedure, I'd want the right charger to do it with.

    They also have a special unit to do the capacity test, which drains at a calibrated rate and also has a timer.
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