How to mothball a depleted battery bank

I have just bought a new battery bank, so what do I do with my old battery bank.  It was 66,240 Wh but I reduced it to 44,160 Wh after removing bad batteries, so probably left about 6,000 Wh usable in the remaining batteries.  

What should I do with them, I was thinking of using a spare Flexmax 80 controller and a single 325 Wp solar panel to tick them over and keep them mothballed until I make up my mind what to do. My gut says scrap them right away and store the flexmax 80 controller.  

I have a lorentz PS6000 DC pool pump, perhaps that would be a good use for the spare charger and batteries.


  • BB.BB. Super Moderators, Administrators Posts: 28,998 admin
    More or less, if you keep them on a minimum 2% rate of charge (solar array), already charged batteries should be happy until use (or die).
    • 6,000 WH * 1/0.77 panel+controller deratings * 0.02 rate of charge = 156 Watt array minimum
    You can get a "cheap" PWM or MPPT controller to float that size battery bank.

    If the 2% rate of charge cannot keep your bank topped off--Then off to the recyclers.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,238 ✭✭✭✭✭
    When you bought the new batteries, you likely paid a "core charge" for the recyclable part of the batteries, and if you traded in your dud batteries, you could have avoided the $40 core charge / battery

    Sometimes you can still sell them at the recycle yard $10 ea.  but keeping old batteries around on float, and watering them till they die completely, is a lot of work.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • t00lst00ls Solar Expert Posts: 200 ✭✭✭
    just my opinion
    I dont know how old the batteries are, but as most of us on here know, the reason batteries die is usually from sulphation

    when I bought my t-105s they had the gray look on the inside, after having done an equalize charge several times, the now have that chocolate brown color inside

    I believe the gray color is associated with sulphation....please correct me if I'm wrong....but before when they were gray, the charge would last very long

    since I bought the first 2 banks, I have added a third ( yeas I know ...dont mix old and new) but....but, I ran them for a while before doing an equalize charge on them.....didnt seem to make much difference on the amount of time before the whole system needed to recharge
    so, I disconnected the first 2 banks and did a few equalize charges on the new bank, plus when the sun was out, I let the new one charge by itself
    now it takes longer to get down to 48.3 between charges and the inside of the new bank is getting that chocolate brown color inside

    trojan recomends a higher bulk charge setting of 59.3 and equalize at 64 for the t-105....I set mine at 60 and left the 64

    sometimes a sulphated battery  just need to get the fluids mixed really good, which is what an equalize charge will do...sometimes just one wont  2 or 3 in a row
    and you really need to do those in stages several hours apart to allow the battery to cool, otherwise you cook the plate material off the plates

    SG temperature compensated and at rest for a few hours is the key...48v bank should read 1.277 in each cell @50,93v or each 6v battery 1.277 @6.37v

    so IMHO  you might be able to get those batteries back to life depending on how old they are
  • t00lst00ls Solar Expert Posts: 200 ✭✭✭
    what I do know: charging to 100% at a lower amperage over a longer period of time will make the charge and battery life last longer...dont know why....everything I have read and seen tells me this
  • BB.BB. Super Moderators, Administrators Posts: 28,998 admin
    When you charge >~90% state of charge, with lead acid batteries you are getting into the 'gassing' range.

    When you gas batteries, is eroded the plates, breaks the water into hydrogen and oxygen (need to add distilled water back in), gassing can carry electrolyte mist out of the battery caps and corrode nearby cables/connections/"rotten egg smell", etc.), Oxygen forms on the positive plates which corrodes the positive plate grid, and about 1/2 the charging energy goes into heating the battery (battery that is 10C/18F warmer than room temperature ages about 2x faster).

    Yes, going to ~100% state of charge seems to be needed for lead acid batteries (gassing mixes the electrolyte, helps shed inactive plate material, opens pores in the plates for more active area)--But doing that once or several times a week is about all you need to do that.

    Flooded cell deep lead acid batteries need EQing (roughly once a month...), but EQing is hard on the batteries (heat, gassing, etc.). It is the nature of the beast.

    I am certainly not a battery or chemical engineer... Just the basics I have picked up here over the years. You read enough, and it seems like batteries will never work.

    But they do. Batteries age from the day they are made. Hot batteries perform somewhat better (within reason), but age faster. Cold batteries age much slower, but do not output quite as much current/total energy when cold.

    Your batteries will either age to death, cycle to death, or be "murdered" by improper charging/under or over charging/lack of maintenance or many other factors (not using pure distilled water, not adding water and letting plates get exposed, adding too much water and batteries burp electrolyte out the caps, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richardimorserichardimorse Registered Users Posts: 88 ✭✭
    They are the heavy Ritar RA12-230DG Gel batteries, So being Gel limits what you can easily do, EQ charge is same as normal recharge voltage any action will be messy and involve breaking open the battery seals, given that "IF" I decide to work out how to break one open, I may be faced with dryout as the main problem so adding electrolyte might be a first step, then going for a high EQ charge anyway given that I have started to turn them into wet LA batteries by topping them up might be the next step, all seems like a lot of hard work.
  • t00lst00ls Solar Expert Posts: 200 ✭✭✭
    yeeeeeah, those are a completely different animal

    you can still run an EQ charge on them, you just have to do it at lower amps and keep them cool

    I have heard that you can add sulfuric acid to them along with a gelling agent....usually it is silica that they use as a gelling agent....but I dont know if it will work as they are sealed up now

    good luck

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