Replacement for non hybrid battery in the trunk?

Discussion in 'Generation 1 Prius Discussion' started by War_Destroyer, Jul 24, 2026 at 12:38 PM.

  1. War_Destroyer

    War_Destroyer Junior Member

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    2002 Prius
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    ----USA----
    I my battery finally going bad? Yesterday my little brother was driving my mom around when apparently the car stalled in the middle of the street. The only thing my little brother noticed besides the car being more sluggish than usual is that the center console display turned white when the car stalled. He was able to restart the car and limp it home.

    Torque Pro found codes related to the hybrid battery, which also needs work, but I noticed that the battery voltage for what I assume is the trunk battery rests a 9.6v when I turn the key to position two, but jumps to 14.1v when the car is actually running. Is this too much of a voltage swing meaning that the battery is bad? Do you guys have a recommended replacement?

    IMG20250320145207.jpg
     
    #1 War_Destroyer, Jul 24, 2026 at 12:38 PM
  2. Trombone

    Trombone Active Member

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    For the 12V, I've used Interstate. Any good case size 51R battery will do. You may have to shim the bottom about 1`". Domestic battery will need terminal adapters like these: https://tinyurl.com/32ddyv77

    For the HV, I have this one installed: https://greentecauto.com/hybrid-battery/toyota/prius-hybrid-batteries/toyota-prius-2001-2003/toyota-prius-gen-1-new-cell/
    Greentec has a facility in LA: https://greentecauto.com/locations/los-angeles/
    They also do a mobile install. I paid $75, well worth it.

    Good luck, and let us know how it turns out.
     
    #2 Trombone, Jul 24, 2026 at 3:18 PM
    Last edited: Jul 24, 2026 at 3:55 PM
  3. Trombone

    Trombone Active Member

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    As for your voltage readings on the 12V, conventional info says you need 11+ volts to boot the hybrid system (i.,e., start the car), but I've observed that lower voltage will work. If you get started with 9.6, more power to you (double meaning intended!). On my '02, the 12V readout is 13.8 volts when car is "Ready."
     
    #3 Trombone, Jul 24, 2026 at 3:30 PM
    Last edited: Jul 24, 2026 at 4:17 PM
  4. Trombone

    Trombone Active Member

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    Resting voltage on my 12V is 12.4. That’s with everything off, but presumably incorporating whatever parasitic drain is occurring. The 12.4 is what my ScanGauge is reading; a more accurate measurement would be directly off the battery terminals, and would probably read higher by .1 or .2 volts.
     
    #4 Trombone, Jul 24, 2026 at 3:37 PM
    Last edited: Jul 24, 2026 at 7:44 PM
  5. ChapmanF

    ChapmanF Senior Member

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    9.6V resting voltage on a 12V battery means at the very least that it is very deeply discharged.

    After a long rejuvenating spell on a good battery charger, I'd unhook it and check again. If it holds up decently after, that could have been all it needed. If it's down sub-12-volts again in short order, it's toast.
     
    #5 ChapmanF, Jul 24, 2026 at 5:56 PM
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