Traction battery discharge current

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by PriusII&C, Aug 3, 2025 at 7:12 PM.

  1. PriusII&C

    PriusII&C Active Member

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    I'm in the process of reconditioning my traction battery, and already massed up the first discharge. Forgetting to change light bulbs at 196V and 140V, I discharged the battery pack all the way down to 134V with 2x200W light bulbs. The starting current was 1.66A at 234V, and ending current was 1.222A at 134V.

    How bad could this be to the battery? What are the signs that indicate the battery pack (or some cells) are negatively affected?

    I know I can check the battery capacity after putting the car in operation condition, but that will be a few days away.
     
    #1 PriusII&C, Aug 3, 2025 at 7:12 PM
  2. Brian1954

    Brian1954 Senior Member

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    The hybrid battery should be fine. Just do the next charging cycle with the grid charger.
     
    #2 Brian1954, Aug 3, 2025 at 7:25 PM
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  3. PriusII&C

    PriusII&C Active Member

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    Thanks. That's what I am doing now.
     
    #3 PriusII&C, Aug 3, 2025 at 7:35 PM
  4. PriusCamper

    PriusCamper Senior Member

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    Happens to all of us sooner or later... Fortunately with light bulbs the amount of resistance and amp drain is based on the temperature of the filaments in the bulbs.

    I even once accidentally drained a Honda Hybrid pack down to zero volts on stage one, but because the filaments in the light bulbs were not lighting up and running cold it meant that amp load on the drained pack was very low and soon as I realize what happened I put it back on the high voltage trickle charger and voltage went back up super fast in the pack and no long term damage was done.
     
    #4 PriusCamper, Aug 3, 2025 at 8:44 PM
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  5. PriusII&C

    PriusII&C Active Member

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    You made me feel better.:)
     
    #5 PriusII&C, Aug 3, 2025 at 9:03 PM
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  6. ChapmanF

    ChapmanF Senior Member

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    It would be even more fortunate if a light bulb's dependence of resistance on filament temperature went the other way.

    Inconveniently, the coefficient is positive: the filament resistance rises (by a lot) as the temperature goes up toward the light-emitting range. When cold, it has a very low resistance and will pass more current than you expect, not less.

    That's a useful thing about light bulbs if you want to build a dim-bulb tester for working on vintage hi-fi gear, but it doesn't end up helping you in a battery-discharge application.
     
    #6 ChapmanF, Aug 3, 2025 at 9:49 PM
  7. PriusII&C

    PriusII&C Active Member

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    True.

    However, in hybrid battery discharge process, the filament resistance decrease is a result of battery voltage drop. As a net result, the current still drops. Not as much as with a negative TCR, it still drops nevertheless.
     
    #7 PriusII&C, Aug 3, 2025 at 10:45 PM
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