Just Installed BM-2 Battery Monitor and NOCO On Board Charger

Discussion in 'Gen 5 Prius Main Forum' started by VelvetFoot, Dec 9, 2025 at 9:06 AM.

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  1. Gokhan

    Gokhan Senior Member

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    Same with Gen 4, which has an identical BMS. It goes up to 14.4 V, but it is usually 14.1–14.3 V. The battery SOC will affect the actual voltage.
     
    #21 Gokhan, Dec 10, 2025 at 6:18 PM
  2. VelvetFoot

    VelvetFoot Active Member

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    First dip, 5 hours after stop. Probably EVAP pump. Hopefully, one or two shots and over, 'cause it does cause a step down in voltage.

    upload_2025-12-10_19-34-42.png
     
    #22 VelvetFoot, Dec 10, 2025 at 7:34 PM
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  3. Gokhan

    Gokhan Senior Member

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    Yep, that’s just EVAP, nothing to worry about.

    Gen 4/Gen 5 parasitic drain is mostly an urban legend or myth. The main reason for Gen 4/Gen 5 battery failures is the fact that the BMS doesn’t charge much during warmer months, and if you don’t drive the car frequently for long distances, that could result in battery failures.
     
    #23 Gokhan, Dec 11, 2025 at 2:31 AM
  4. VelvetFoot

    VelvetFoot Active Member

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    There were 3 tiny dips in half-hour intervals overnight, starting an hour after the probable EVAP pump. Perhaps related?. Makes you wonder what they are. :)
    I might see if my security camera in the garage can pick up the sound of the EVAP pump, lol.

    upload_2025-12-11_6-42-50.png

    upload_2025-12-11_6-43-23.png
     
    #24 VelvetFoot, Dec 11, 2025 at 6:43 AM
  5. Gokhan

    Gokhan Senior Member

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    They could be EVAP or other things. It is nothing to worry about.

    Incidentally, the dips for my AGM battery are shallower than for your flooded-cell battery because of the lower internal resistance of an AGM battery.
     
    #25 Gokhan, Dec 11, 2025 at 2:13 PM
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