Is my battery bank dead from sitting idle for a year?

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klikitykev
klikitykev Registered Users Posts: 3
I have a set of 12v Sun Xtender sealed Lead Acid batteries in my battery bank wired together in parallel pairs (24v). They had been working fine until I went away for over a year and they sat inactive. The voltage now reads as about 7-8v per pair and they don't seem to want to recharge now they are reconnected to the solar array. I have read that you should never let batteries go below 50% but it seems they are well below that. 

Are they mostly likely dead but retrievable, or temporarily dead and somehow retrievable?
 
Thanks in advance for any kind advice. 
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    Likely dead, but you should give it a try to rejuvenate them...

    Most charge controllers won't try to charge a battery that is that low. I suggest putting them on a dumb charger, individually on something like a car charger. Be aware that they may have limited capacity at first, so watch the voltage! Once it gets up to 13-14 volts, I'd pull them off. See what voltage they are holding, then try them back on the solar charger. Go to SunExtender's web site, I think they have a system to do something like an equalizing. Where you hold the voltage at a high level for an extended period of time.

    If you are lucky enough Marc might see this thread and give you some details. I can't imagine them getting to that low a voltage without having some type of load on them.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • klikitykev
    klikitykev Registered Users Posts: 3
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    Thank you so much for replying Photowhit. I will certainly try charging them individually and see if they can be rejuvenated. Fingers crossed. 
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,145 ✭✭✭✭
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    I have a set of 12v Sun Xtender sealed Lead Acid batteries in my battery bank wired together in parallel pairs (24v). They had been working fine until I went away for over a year and they sat inactive. The voltage now reads as about 7-8v per pair and they don't seem to want to recharge now they are reconnected to the solar array. I have read that you should never let batteries go below 50% but it seems they are well below that. 

    Are they mostly likely dead but retrievable, or temporarily dead and somehow retrievable?
     
    Thanks in advance for any kind advice. 

    Keep in mind that 10.5v under load, is "dead" (0% state of charge) on your 12v batteries. Also important: A standing steady-state voltage without a load, of 11.6v is the equivalent of 10.5v under load. Your battery voltage is way down into damage territory. I agree with Photowhit, they would not have gotten anywhere near that low in only one year with zero load.
    There is a factory-recommended procedure for "deep discharge recovery" which can really work well under certain conditions.
    Specifically, which batteries do you have? PVX-_______?
    What is the standing volatge after disconnecting the batteries and letting them sit for a couple of hours?
    How old are they? (The first digits of the serial number indicate the year)
    How many batteries total?
    Are there any signs of bulging on the sides or around the terminals?
    Where are you located?
    Marc

    I always have more questions than answers. That's the nature of life.
  • Intheswamp
    Intheswamp Registered Users Posts: 16 ✭✭
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    I tried reviving a set of four 6-volt Trojan T105s that had been idle a while back.  And, after a couple of weeks of charging, resting, discharging, rinse-repeat, I managed to get one of them to hold at around six volts while the others would never stay much above two volts.  Of course, this set was pushing 19 years old and had sat idle for the last 17 years and none showed over two volts when I started CPR on them.  I'd say you have a better chance than I did to salvage yours.  Reviving them will take time.  One thing that concerns me is that they are SLA batteries, no way to check electrolyte levels or top them off so you don't want to be too heavy-handed with them.  I'm thinking that the aH capacity will be reduced from sulfation, though.  If you do manage to revive them expect a reduced performance.  Plan for the worse, hope for the best.  You've got nothing to lose but time and energy. :)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,474 admin
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    For conditioning Sun Extender/lineline/Concord batteries only--The manual (page 22):

    https://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101F-Lifeline-Technical-Manual-Final-5-06-19.pdf

    Upwards of 3 volts per cell (18 volts @ 12 volt battery)--Should not be done to any other brand/model of lead acid battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,145 ✭✭✭✭
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    BB. said:
    For conditioning Sun Extender/lineline/Concord batteries only--The manual (page 22):

    https://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101F-Lifeline-Technical-Manual-Final-5-06-19.pdf

    Upwards of 3 volts per cell (18 volts @ 12 volt battery)--Should not be done to any other brand/model of lead acid battery.

    -Bill

    Yes, Sir. That is the upper voltage limit for the "deep discharge recovery" procedure, but it is important to be discussed in context. The 3v/cell only applies as part of a procedure when you have the capability of a low, controlled current charge limit with a rising voltage up to 18v.
    While Concorde batteries can easily absorb a 4C to 5C inrush charge current, other conditions must be met - and deep discharge recovery is not one of them.
    Marc

    I always have more questions than answers. That's the nature of life.
  • klikitykev
    klikitykev Registered Users Posts: 3
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    I have a set of 12v Sun Xtender sealed Lead Acid batteries in my battery bank wired together in parallel pairs (24v). They had been working fine until I went away for over a year and they sat inactive. The voltage now reads as about 7-8v per pair and they don't seem to want to recharge now they are reconnected to the solar array. I have read that you should never let batteries go below 50% but it seems they are well below that. 

    Are they mostly likely dead but retrievable, or temporarily dead and somehow retrievable?
     
    Thanks in advance for any kind advice. 

    Keep in mind that 10.5v under load, is "dead" (0% state of charge) on your 12v batteries. Also important: A standing steady-state voltage without a load, of 11.6v is the equivalent of 10.5v under load. Your battery voltage is way down into damage territory. I agree with Photowhit, they would not have gotten anywhere near that low in only one year with zero load.
    There is a factory-recommended procedure for "deep discharge recovery" which can really work well under certain conditions.
    Specifically, which batteries do you have? PVX-_______?
    What is the standing volatge after disconnecting the batteries and letting them sit for a couple of hours?
    How old are they? (The first digits of the serial number indicate the year)
    How many batteries total?
    Are there any signs of bulging on the sides or around the terminals?
    Where are you located?
    Marc

    Hi Marc and thank you so much for your considerate response. In answer to your questions: 
    1. The battery type is PVX-1080T
    2. The standing voltage after a while is 9.9V
    3. The first three digits are 013, so I'm guessing this means they are nine years old
    4, I have a total of eight identical batteries
    5. There is no sign of bulging on the sides or around the terminals. 
    6. I'm located in Kyoto, Japan. 

    I have found the recommended procedure in the manual for deep discharge recovery and am wondering how to do a constant current charge
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,145 ✭✭✭✭
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    Yes, and at 9 years you are approaching the 10-12 year design life. I have a charger that will perform the constant current function - that is why I was wondering where you are. Kyoto is a little too far away from Texas for me to help  :)
    The next best thing is to equalize them as Photowhit suggested. I would do them individually at first. The objective is to apply 15.5v for 8 hours. BUT you need to keep an eye on the temperature and stop the process if you approach about 125F.  Let them cool for a few hours and start again. Don't get concerned if see the current draw climbing - that is what you want. You do not have a charging source big enough to apply too many amps, but the temperature needs to be watched. Your goal is to have a 12.8v standing voltage, measured at least 4 hours after charging. You may find that 4-6 of them have some service life remaining, but low voltage for an extended time is a killer.
    Let me know how it goes!
    Marc Kurth
    Eustace, TX
    I always have more questions than answers. That's the nature of life.