Hybrid cars sitting unused

Discussion in 'General' started by some_other_dave, Jun 10, 2021.

  1. some_other_dave

    some_other_dave Well-Known Member

    I know that the 12V battery in combustion-engine cars can go flat when the vehicle is not driven for a while. Repeated instances of this can damage the battery to the point where it won't take much of a charge any more.

    Does the same sort of thing happen to the traction batteries in a hybrid? If we do get a hybrid, will we need to make sure it gets started and driven periodically? I just recently realized that any new car we get is likely going to sit unused for several months at a time, without even a battery maintainer to help it out.


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  2. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    That's a really good question. Toyota has some procedure for the Prius for long-term storage ,
    but I don't remember what it is.
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  3. Trollbait

    Trollbait Well-Known Member

    Traction batteries aren't starter batteries. Lead-acid batteries need to be kept at 100% charge for the longest life. For the Li-ion and NiMH used in hybrids, they do best at some point below full charge. Exactly where depends on the exact chemistry, but the control software keeps the state of charge in a happy zone for longest life. When turned off, the traction pack is physically disconnected, so there aren't the parasitic losses the started battery is under. The only losses while parked should be from self discharging that all batteries see.

    The hybrid battery should be fine with just taking the precautions for a traditional car when being parked for several months. if you can't use a battery maintainer, you should disconnect the starter battery.
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  4. S Keith

    S Keith Well-Known Member

    Depends on the car/battery/chemistry. Consult the owner's manual.

    Dealer procedure for new cars on the lot or on transport: Ready mode for 30 minutes every two months.

    Owner's manual is not firm in memory, but it's something like, disable smart key system if stored for 2 weeks, Disconnect 12V battery if stored for more than 30 days.

    That's pretty much it. Confirm with your owner's manual.

    Some folks think putting a maintainer on the 12V is fine. It's NOT the same as disconnecting it. If you want to put a maintainer on the 12V, disconnect it first.

    One car that is a real bitch about it is the Ford Escape hybrid. if you fail to disconnect the 12V, the traction battery will deplete. On 05-08, it's not a big deal as they have HV jumpstarters that allow recharging of HV via 12V, but it was removed on 09+. I've manually recharged at least a dozen of them.

    Another consideration is WTF do you do when you return. Here's what I recommend:

    1) fully charge 12V
    2) Do not drive the car. Start and idle car until the engine turns off. Then drive very conservatively.

    The reason for #2 is that it's the period during which the car assesses the battery condition and charge. Allowing it to complete that assessment can help prevent incidents from outlier cells.

    NiMH is way more sensitive to storage and return-to-service issues than Lithium.
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  5. RedylC94

    RedylC94 Well-Known Member

    My understanding is that being parked unused few a few months is normally not a problem for a NiMH hybrid traction battery, assuming it's not in a relatively low state of charge when parked. Periods on the order of a year or years might become a problem, and recharging it is a much bigger deal than charging or replacing a 12v lead-acid battery.

    No, you should disconnect the 12-volt "auxiliary" battery. The traction battery effectively IS the engine-starting battery in conventional hybrids.
    BillLin likes this.
  6. S Keith

    S Keith Well-Known Member

    Ironically, an '09 FEH was just dropped off for this issue today. Owner was instructed to drive it regularly and disconnect the 12V if parking for more than 1 week.

    3 weeks of sitting, and it's sitting at 289V. ICE no-start.

    Battery cover removed, charge points accessed, charged and running.
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  7. RedylC94

    RedylC94 Well-Known Member

    What's that voltage supposed to be?
    Do you feel that battery is near the end of its life?
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  8. S Keith

    S Keith Well-Known Member

    300V resting is dead empty. 315V would be around the low end of acceptable.

    It might be. It's certainly compromised, but it will likely perform acceptably for years/miles if it's not allowed to discharge.
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  9. some_other_dave

    some_other_dave Well-Known Member

    Thanks for the responses!

    BillLin likes this.

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