Remarkable battery voltage disparity?

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softdown
softdown Solar Expert Posts: 3,821 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
Early morning voltage of one is 10.9V. The adjacent, in series, battery reads 12.9V.
The overall series reading is ~49.4V in early AM due to running multiple freezers. The rest of the batteries read ~ 12.4V. I've never seen one battery read so high in the early morning hours (6am) and it is next to a battery that reads extremely low.
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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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
    edited October 2022 #2
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    The early morning reading of 12.9v surprises me most assuming that readings were taken before any solar production.
    Without more info, my first guess is that the 10.9v battery is presenting zero load during the charging period, resulting in a much higher than normal voltage on the next one. In my experience, that 12.9v standing voltage remaining overnight would normally indicate serious overcharging. What batteries are these?
    I always have more questions than answers. That's the nature of life.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    #3
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    Sounds like these 12 volt batteries are in some sort of series configuration, allowing you to take individual voltage readings. Like Mark said one battery is being overworked to compensate for the lazy battery's shortcomings. Average voltage between the two being something like the full bank's voltage.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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