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engine battery if dormant

Discussion in 'Gen 2 Prius Technical Discussion' started by basicperson, May 23, 2008.

  1. basicperson

    basicperson New Member

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    Hello,

    I was wondering, if you parked your car for two or three months without starting, what happens to the engine battery?

    I've seen some posts about the regular 12 volt battery losing charge. This I believe can be fixed by turning off the car key sensor.

    But I'm more concerned about the $4000 engine battery. The engine battery I believe wants to stay around 40%-70% charge at all times. If the car was parked for three months, would that damage the engine battery?
     
    #1 basicperson, May 23, 2008
  2. tochatihu

    tochatihu Senior Member

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    People have left Prius undriven for several months, managed the 12 volt battery in various ways, and then restarted without problems. This is not to say that the NiMH battery does not self discharge. Different designs of NiMH definitely have different self discharge rates, and we just don't know about that for this one.

    Measurements are possible (by people willing and able to tackle high voltage safety issues), but I do not believe that they have been reported.

    The self-discharge risk is perhaps small. The only thing you can do to minimize it is to 'force-charge' the HV battery before storage. That simple procedure has been described here before, along with the obligatory cautions.
     
    #2 tochatihu, May 23, 2008
  3. qbee42

    qbee42 My other car is a boat

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    The battery to which you refer is usually called the HV battery, traction battery, or sometimes the hybrid battery. Since it has no connection with the engine it is a bit confusing to call it the "engine battery".

    The HV battery is NiMh, and as such, has a very low self discharge rate. It is disconnected when the Prius is not powered up, so there is no problem leaving it for two or three months. As the other poster suggested, if the SOC is low, you might want to drive it around the block a few times or perhaps do a forced charge prior to storing.

    Tom
     
    #3 qbee42, May 23, 2008
  4. jayman

    jayman Senior Member

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    If you intend to leave the Prius for 2-3 months, I strongly recommend you invest in an automatic battery tender. I use VDC Electronics Battery Minder, which also desulfates the battery, but there are other choices out there

    The 12 vdc Prius battery is expensive, as you can't go to Autozone and get a generic battery. It's sealed and has a vent tube connection. It also doesn't tolerate being chronically discharged.

    I haven't heard of any issues with the NiMH Traction battery. Once you power off the car, the NiMH relays are opened, so only self-discharge can occur.
     
    #4 jayman, May 23, 2008
  5. David Beale

    David Beale Senior Member

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    Toyota says you can leave the NiMH battery unused for six months. They recommend driving or running the car after that time. Sorry, don't remember where they said this, check your owners manual.
     
    #5 David Beale, May 24, 2008
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