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Time to Replace 12V?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Peter Chicarielli, Mar 2, 2023.

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  1. Peter Chicarielli

    Peter Chicarielli Junior Member

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    Hello!

    My Gen 2 Prius has been dying as soon as I arrive to the destination and turn the car off. I assume it's time for a new battery, but was curious if there are any tests I should do first. I bought the 12V back in Nov 2019, so it's almost 3.5 years old. My ACC reading is 12.4 and 13.9-14 while driving.

    I'm mainly trying to hear back from you all because I paid $138 for the 12V back in 2019 and now it's $289!

    Should I take it to Pep Boys and get the full battery/alternator test?
     
    #1 Peter Chicarielli, Mar 2, 2023
  2. ColoradoBoo

    ColoradoBoo Senior Member

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    lol...if you find an alternator then you don't have a Prius!! (We don't have one...the high-tech ECU, also called ECM, charges our 12-volt when needed using some voodoo magic I don't understand!)

    Do you have any lights on the dash like check engine or the red triangle?

    Parts stores can tell you the health of the 12-volt but can't test the starter or alternator health.
     
    #2 ColoradoBoo, Mar 2, 2023
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    You could get something like a Solar BA9 (around $60 USD) and test it. Pep Boys will likely use something pro-level but similar.
     
    #3 Mendel Leisk, Mar 2, 2023
  4. PriusCamper

    PriusCamper Senior Member

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    Your battery is too new to go go bad, but it does happen... But to be sure put the 12v on a smart charger that goes up to at least 8 amps for 12 hours. Prius suck at keeping their 12v charged all by themselves.

    As for tests, when you shut the car off watch the speedometer. If the shut off sequence is working normally the gear shift indicator on that screen will shut off last, but if you have some loose connection issues with the 12v the whole car will go dead all at once at shut off.
     
    #4 PriusCamper, Mar 2, 2023
  5. Peter Chicarielli

    Peter Chicarielli Junior Member

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    Thanks for the replies! The positive terminal needed tightening, as well as the metal bar that holds the battery in place. Too many speed bumps in my area!

    As soon as I hit the power button, it immediately dies. Everything is off.

    BUT! I tightened up the 12V and left the cables connected between cars for about 10 minutes. Disconnected and ran it in maintenance mode for 45 min so the engine remained running. After that I drove it for 30 minutes. Before the drive, I noticed that it did not die when turning it off. After the drive, it was the same.

    I let it sit for about 2 hours and it's still working. I'm kind of shocked that the terminal posts just needed a tightening since they were 100% making contact. I don't know much about this stuff. I wasn't even 100% if there was an alternator or not haha.

    Hopefully after a cold night, it starts right up. If not, maybe I'll try that smart charger for 8 hours if I can find one.
     
    #5 Peter Chicarielli, Mar 2, 2023
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