Not starting…which battery needs changed?

Discussion in 'Gen 2 Prius Main Forum' started by Lhuber, Aug 29, 2021.

  1. Lhuber

    Lhuber Junior Member

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    Our 2008 Prius randomly needs jumped. How do we know if we need to replace the 12 volt or the front battery?
     
  2. MickyMatter

    MickyMatter Active Member

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    If you need jump-starting assistance, the 12 V auxiliary battery is too weak - perhaps it is too old, or it is discharged by a leakage current.

    As a kind of first aid measure, you can support the 12 V battery with a small lithium power bank (see attached pic for example, they can also charge USB devices) with 12 V connector, because the Prius needs just a little bit of power to start the computer. Then the Prius can charge the 12-V battery with the 200-V battery. (And the 200-V battery with the engine. And the engine would start before the 200 V battery is too low).
    View attachment 215491
     
    #2 MickyMatter, Aug 29, 2021
    Last edited: Aug 29, 2021
  3. TMR-JWAP

    TMR-JWAP Senior Member

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    There is no battery in the front of the car like most normal internal combustion engine vehicles. Your 12v battery is located in the trunk area at the very rear on the passenger side, under the small floor cover. If your car won't power on, it's likely that battery is discharged or has a poor connection somewhere. It may or may not need replacing, that would depend on test results. Sometimes silly things happen and the battery gets discharged due to lights being left on or the radio being played for a long time with the car not in 'Ready' mode. In a Gen 2 Prius, the 12v battery is charged only when the car is in 'READY'. Kind of like a ICE car can only charge it's battery when the engine is running so it can spin the alternator, the Prius can only charge the battery when HV power is available at the inverter.

    Odds are good that if you're unfamiliar with the actual battery location, you've never had to mess with it before. In that case, unless this car was a recent purchase, it's also likely the battery is very old and needs to be replaced, regardless.
     
  4. Another

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    Charge the 12v battery fully with an external charger, then do a load test on it. If it fails the load test, replace it. If it passes, then look for other causes.
     
  5. Calimobber

    Calimobber Member

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    If you pop the hood and open the fuse box in the back right there is a red 12v bolt you can clamp on jumper cables to and that will power up the system and then you can start the car. Like othere have said your battery may be getting old and need replaced but it might be okay for now. Ive killed mine a few times by leaving headlight on or dome light but once charged its fine.

    make sure you drive at least 30min+ to let the battery charge up more, I might even go for an hour. You can also get a 12v battery charger and hook it directly to the battery and charge overnight.
     
  6. SFO

    SFO Senior Member

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    When was the last time it was replaced?

    How many hours per week are you currently driving this vehicle?
     
  7. sam spade 2

    sam spade 2 Senior Member

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    The "jump" you are doing is with a 12 V battery.......to the 12 V system in the car.
    Which one do YOU think needs to be replaced ??
    This is not a hard question. :)

    There also could be a loose connection ......and the charging voltage needs to be checked too.
     
  8. Lhuber

    Lhuber Junior Member

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    But here’s the thing… the red triangle has been coming on more often after we jump it… but then disappears once it’s running. Also after it’s jumped we drive it for a good 30 min…. Turn off the car, then try to start it again and nothing…. Needs to be jumped again. Some have said the Hybrid battery needs replaced. We are just confused.
     
  9. bat4255

    bat4255 2017 Prius v #2 and 2008 Gen II #2

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    Again, how old is the 12v battery.

    it sounds like it's done and needs to be replaced.
     
  10. TMR-JWAP

    TMR-JWAP Senior Member

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    These are perfect indicators that the 12v battery will no longer take a charge. It's time to replace it.

    On another note, the prius charging system is different from a normal non-hybrid style car. It would take several hours of driving to actually charge a (good) fully depleted 12v battery.

    Once you start the car, the Inverter has an internal circuit called a DC/DC Converter. This circuit converts the HV battery power (220ish volts) into about 14 volts, which is then used to power the 12v system (and charge the 12v battery). Very similar to how an alternator works. Unfortunately, the 12v battery appears to not be charging.

    The next time you get your car running, drive to the nearest NAPA and have them test your 12v battery. They'll connect an electronic tester and with 99% certainty, will tell you the battery is bad. They normally stock a replacement on the shelf (at least they do near me). They will probably even install it for you. Just remember, it's in the trunk on the passenger side under the small cover.

    In the link below, the first battery is the 12v battery you need. The second battery (orange) is a Dorman Products replacement HV battery.

    https://www.napaonline.com/en/search?text=batteyr&referer=v2
     
    #10 TMR-JWAP, Sep 1, 2021
    Last edited: Sep 1, 2021
  11. ChapmanF

    ChapmanF Senior Member

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    Once the 12 volt battery is taken care of (replaced or well charged and holding it), if the red triangle comes on, find out why.

    Then post the trouble codes here, and we'll know something.
     
  12. Another

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    interesting, until I looked today at these 12v batteries, I didn’t know Napa also sold HV Prius batteries by Doorman for $1600.
     
  13. dolj

    dolj Senior Member

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    The Dorman batteries are reconditioned secondhand ones. These days they are about as reliable as all other secondhand refurbs.
     
    #13 dolj, Sep 2, 2021
    Last edited: Sep 2, 2021
  14. sam spade 2

    sam spade 2 Senior Member

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    Here's the thing:
    The 12 V battery can easily be tested.
    IF the hybrid battery was bad, it likely wouldn't run at all.......or very poorly.
    Those who have pointed you toward the hybrid battery are NOT doing you any favors.
     
  15. aplus

    aplus New Member

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    Just wanted to add that if you find that the battery is not holding a charge or if it needs to be jumped every time in order to start, you'll want to replace it. It's not as straightforward on cars where the battery is under the hood, so I found this video helpful:
     
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