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Replace the 12v Bat. or not is the question.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Fartsalot, Nov 2, 2018.

  1. Fartsalot

    Fartsalot Junior Member

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    Since the car is a new to me item I checked the Bat voltage thru the diagnostic checking method and found the voltage to be 11.8 when it is under a load and using that figure the Bat. needs to be replaced.

    When I check the voltage from the Battery with my volt meter the voltage under the same electrical load is within specs. Without any load on the Battery the voltage is 12.4 taken right off the Battery terminals.

    Should I replace the battery or do I consider the numbers to be off a bit by going thru the diagnostic check system. Other option would be to keep a close watch on the Battery but what set of readings to I follow.
     
    #1 Fartsalot, Nov 2, 2018
  2. SFO

    SFO Senior Member

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    How many mins/hours per week do you drive?

    Can you read the date code on top of the battery?

    Do you have a smart charger?

    I would keep a close watch on it. It sounds like the 12v has weakened some, but is still usable.

    If this vehicle is mission critic (job, school, doctor, etc), you may want to replace it depending on the battery age or your stress threshold.

    If not mission critical, then wait for low 12v symptoms to appear or a code to be thrown.
     
    #2 SFO, Nov 2, 2018
    Raytheeagle likes this.
  3. Fartsalot

    Fartsalot Junior Member

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    SFO Service Critical status

    This car was serviced strictly by a toyota dealer so I have all the service records down to a low tire issue that was done on this vehicle. I found out that the Battery was replaced about 4 years ago, I also thought the battery is on the edge of serviceable vs just replacing it. What threw me off was the difference in voltage readings at the battery and diagnostic prochedure.

    After reading your post,,, I'm going to replace it, easy and simple to do and not a big costly deal either and besides I have no way to read codes that show up anyway.

    Question ?? When I change the battery do I need to disable the smart key system?? Or do I just change it like I did with my Honda Civic.
     
    #3 Fartsalot, Nov 2, 2018
  4. ChapmanF

    ChapmanF Senior Member

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    You saw a difference of 0.6 V from the battery itself to the diag screen on the MFD. That's pretty consistent with what I always see, so don't be surprised if you see the same with a new battery. The MFD is downstream of a handful of connectors, fuse links, and fuses with associated voltage drops.

    -Chap
     
    #4 ChapmanF, Nov 2, 2018
  5. SFO

    SFO Senior Member

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    You may not have to replace, if you drive enough on a regular basis (which is why I asked about number of mins/hours per week)

    No need to disable the smart key system under the steering wheel.

    There are many ways to approach a replacement, some go straight for disconnecting the negative cable at the body (and then at the negative terminal, followed by the positive terminal), others disconnect the two (2) positive connectors first, then the negative cable from the body, and then at the negative terminal, followed by the positive terminal.

    Bet there is a write up, or a video somewhere.

    Have you already picked out a battery?
     
    #5 SFO, Nov 3, 2018
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  6. bisco

    bisco cookie crumbler

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    If 12.4 was measured after everything off for a few hours, I’d jut keep an eye on it
     
    #6 bisco, Nov 4, 2018
  7. Fartsalot

    Fartsalot Junior Member

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    I decided to install a Optima and not half to worry with the Battery,,,,I use the car daily in my work and reliability is important since time is money for me anyway.

    For some reason I enjoy driving this car over my F250 Diesel pickup,,,
     
    #7 Fartsalot, Nov 5, 2018
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