Most efficient time to replace older batteries?

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softdown
softdown Solar Expert Posts: 3,824 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
6am voltage runs ~ 49.1 volts. Batteries are getting pretty old. 

But I think money is saved by continuing their use until 6am voltage runs ~ 48.8 volts. Roughly speaking. 

I have four "automotive grade" 24 volt lithium batteries waiting in the wings. For the past ~ 3 1/2 years. Their voltage has dropped from ~ 26.3 volts to 26.2 volts over that period. They store quite well. 
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • softdown
    softdown Solar Expert Posts: 3,824 ✭✭✭✭
    #3
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    Marc Kurth said:
    Why not use them until they can't provide enough power to keep the inverter running? I can't count the number of customers who called me for new batteries but got another season or two out of their old battery bank by simply lowering the inverter LVCO setpoint. 
    Customer: "But it's bad to run them down that far."
    Me: "Ummm......... you were about to toss them and buy new batteries anyway.”
    That is not what I expected from a battery supplier.Happy New Year!!!
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • JRHill
    JRHill Registered Users Posts: 285 ✭✭✭
    #4
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    To me it's that old batteries work until they don't meet your power storage needs. Wow, that was profound (wink).
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
    #5
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    softdown said:
    Marc Kurth said:
    Why not use them until they can't provide enough power to keep the inverter running? I can't count the number of customers who called me for new batteries but got another season or two out of their old battery bank by simply lowering the inverter LVCO setpoint. 
    Customer: "But it's bad to run them down that far."
    Me: "Ummm......... you were about to toss them and buy new batteries anyway.”
    That is not what I expected from a battery supplier.Happy New Year!!!

    If we are talking bout the Fullriver 8Ds, run them down as low as 42v under load but not lower. When you draw them down to 42v, expect them to rebound to 46.4v after a couple of hours of no load. 
    Remember that 42v under load and 46.4v no load are both 0% SOC.
    Happy New Year back at you!
    Marc
    I always have more questions than answers. That's the nature of life.
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  • SumPower
    SumPower Registered Users Posts: 48 ✭✭
    edited January 5 #6
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    Marc Kurth said:
    softdown said:
    Marc Kurth said:
    Why not use them until they can't provide enough power to keep the inverter running? I can't count the number of customers who called me for new batteries but got another season or two out of their old battery bank by simply lowering the inverter LVCO setpoint. 
    Customer: "But it's bad to run them down that far."
    Me: "Ummm......... you were about to toss them and buy new batteries anyway.”
    That is not what I expected from a battery supplier.Happy New Year!!!

    If we are talking bout the Fullriver 8Ds, run them down as low as 42v under load but not lower. When you draw them down to 42v, expect them to rebound to 46.4v after a couple of hours of no load. 
    Remember that 42v under load and 46.4v no load are both 0% SOC.
    Happy New Year back at you!
    Marc
    Good post Marc K!
    Basically, run them and maintain them like you want them to last. But don't be afraid to kill them as you are replacing them anyway.
    And with your post title, "Most efficient time to replace older batteries?" Is when they have exhausted there usefullness, Run them till you know they are dead.
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  • JRHill
    JRHill Registered Users Posts: 285 ✭✭✭
    #7
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    This Is out of line with out context. 
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.
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