Notes on parallel / series connection

  • What to pay attention to when using batteries in series or parallel?

  • Connected in parallel:
    1) Recommend to fully charge the batteries before parallel connection.
    2) The voltage of the two batteries should be the same (error range 0.1V).
    3) The cable length between batteries should be the same.

    Connected in series:
    1) The nominal capacity of the two batteries should be the same (small errors allowed).
    2) The cable length between batteries should be the same. 

  • When Two 12v 100AH AO batteires are connected in parallel, shold the BMS via bluetoth read the same?  I am seeing the lead battery (the one with the postive connected to the RV) show the voltage drop and amperage loss but the the "rear" battery (the one with the ground going to the chasis) maintain at 100%.


    Battery 1Batteries in Parallel.


    Battery 2


  • Further testing

    1) Isolated the one battery "non-reporting battery."  It works. BMS reads correct voltage.

    2) Swap batteries so "non-reporting battery" is "first".  Now it read correctly however "trailing battery now reads some amprage but differnet than the first battery.

    Please explain.

  • Hi Doug, Nice wiring job! I see you used some beefy cables and wired your batteries correctly for balanced charging.

    A note about your battery readings, it appears your "non-reporting battery" at the time you took those pictures, shows your charge switch "closed" when it should be open (probably a cell reached overvoltage during charging) and your Protection State is "opened" when it should be closed, causing no power to or from battery. Should have resolved itself after the high voltage of the one cell got back into normal range. All part of the safety circuitry that make these batteries truly unique! Lastly, charge/discharge amperage will always be slightly different due to individual differences in battery impedance. It's all good!

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