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Is My Hybrid Battery Going Bad?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by mikednpv, Oct 3, 2012.

  1. mikednpv

    mikednpv Junior Member

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    I have a Gen II Prius with 197,000 miles. Typically I get 43-45 mpg. The last two tanks have averaged about 37 mpg. Also the battery seems to drain faster.
    I think I know the answer but would like confirmation.
    Mike
     
    #1 mikednpv, Oct 3, 2012
  2. Britprius

    Britprius Senior Member

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    First check the voltage of the 12volt battery as there have been reports of this in some circumstances causing mpg loss.

    Does the state of charge fluctuate rapidly going from 2 pink bars to 7 green and back again quickly.
     
    #2 Britprius, Oct 3, 2012
  3. mikednpv

    mikednpv Junior Member

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    The 12 V battery was replaced with an OEM batt about 6 months ago. I have not checked it with a DVOM but I'm not seeing any bad 12 V behavior.
    The SOC for the HV battery does seem to drop quickly to two pink bars. I don't notice any difference in the charging rate from pink to green.
     
    #3 mikednpv, Oct 3, 2012
  4. Britprius

    Britprius Senior Member

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    Rapid changes in the state of charge is usually the first sign of failure but this is usually in both directions if the capacity of the battery is low. Empties quickly then appears to charge quickly.

    You can check the 12 volt using the MFD just to eliminate it. You would not be the first to have a faulty 12v battery
     
    #4 Britprius, Oct 3, 2012
  5. mikednpv

    mikednpv Junior Member

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    Well, I live on a large hill that typically has my battery fully charged by the time I get to sea level so it's hard to notice if the charging rate is quicker than normal. I'll try to notice when I'm on flat ground. Thanks!!
     
    #5 mikednpv, Oct 3, 2012
  6. J Moberly

    J Moberly New Member

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    Well what are the symptoms of a battery going bad if this is not it?
     
    #6 J Moberly, Oct 24, 2013
  7. Britprius

    Britprius Senior Member

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    As I explained in post (4) rapid changes in the level of charge on shown on the MFD, both in the rate of charge and discharge. By this I mean almost instant change in charge level from 5 or 6 charge bars to 1 or 2 then swinging back to 5 or 6 bars just as quickly.
    Discharging fairly quickly when the car is first used from cold is normal operation particularly if the AC is used. The Prius uses a lot of battery assist while warming the engine quickly lowering the state of charge.

    John (Britprius)
     
    #7 Britprius, Oct 24, 2013
  8. ericbecky

    ericbecky Hybrid Battery Hero

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    I would encourage you to check other general things first.
    Air filter
    Spark plugs
    Oil level
    Tire pressure

    And if you still are concerned that it is the battery, if have someone near you that can do a HV battery balance, that may be a good way to go first.

    Where are you located?
     
    #8 ericbecky, Oct 24, 2013
  9. wjtracy

    wjtracy Senior Member

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    I agree with BritPrius if A/C on, you can get too low charge pretty quick on start-up. In general A/C drains the batt and the heater charges it up (due to running engine for heat). Also many of us have installed Optima 12v battery, so consider how old that 12v is, and check out the diagnostics test posted here for the 12v.
     
    #9 wjtracy, Oct 24, 2013
  10. J Moberly

    J Moberly New Member

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    I had my 12v battery tested last night (just bought the car day before last), it's good. Also the air filter, it's good. There are not trouble codes stored (pulled from old odbc reader). I'm taking the car back to this shady used car dealer, I PRAY he will take it back. In California you are supposed to be offered a 2 day return option for a fee IN WRITING. I was never provided that.
     
    #10 J Moberly, Oct 25, 2013
  11. nh7o

    nh7o Off grid since 1980

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    Note that a generic obdII reader will not give you much info about a Prius, or in some cases it will give false readings. You must use a Prius specific reader. What exactly is happening with the car?
     
    #11 nh7o, Oct 25, 2013
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