Replace 12v battery?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Lord Byron, Sep 5, 2019.

  1. Lord Byron

    Lord Byron Member

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    My 08 gen2 has the original 12v battery.. going on 11 years and 206,000mi. Should I replace it? It seems to be ok, but from what I’m reading, that’s a looong time. Could it be having problems that I’m not aware of?

    Also, I’m running the original battery pack and cooling fan (cleaned out the fan for the first time about 6 months ago, just shy of 200,000).
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I suggest you measure voltage across the 12V battery first thing in the morning before the car has been driven. 12.9V is fully charged. 12V is discharged. Your decision to replace the battery should be based upon your measurement and your desire to avoid a common reason for no-start.
     
  3. dolj

    dolj Senior Member

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    • No, not necessarily;
    • That maybe so, but you are obviusly doing something right. I'm not a big fan of replacing things that are not broken. Take Patrick's advice above and proceed as necessary.
    • No, if you were having problems, you would be aware.
    Fantastic. Keep doing what you're doing.
     
  4. Lord Byron

    Lord Byron Member

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    I had no idea how to run a battery diagnostic until now. Never knew the system check mode existed! First thing in the morning.. with first power button, it comes up 12.3V. When I hit power button again it goes down to 11.9 and with pressing break and power to turn car on it goes up to 14.2. I assume that’s pretty much what I want it to be? If so, I’m at 11 years & 207,000mi with the original battery.
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    It appears that your battery is getting marginal but is still functional. You can continue as-is, or can decide to do a preemptive replacement, its up to you. You've got cold winters in your area, that is the usual season when the battery decides to fail.
     
  6. sam spade 2

    sam spade 2 Senior Member

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    Just barely. I vote to replace it now when you can do it at a time that is convenient for you.

    Note: once the car goes "ready", you are not measuring the battery but the charging system inverter output.
     
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  7. bisco

    bisco cookie crumbler

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    only if you don't want to wind up stranded somewhere as i recently was :oops:
     
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  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Some owners are more worried about squeezing out the last bits of life from the 12V battery while others might be more interested in not being stuck in a snowy parking lot in the dead of winter. The OP has sufficient info to make a determination of what works for him.
     
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  9. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Google a few of these:

    Solar BA9
    Ancel BA101
    Foxwell BT100
    Autool BT360
     
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  10. Lord Byron

    Lord Byron Member

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    I think I’m going to go ahead and replace it soon.. I would rather do it now on my terms than when it decides.. although I am curious to see how long I can push it. Thank you all!
     
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  11. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Yeah it's waaay overdue. ;)
     
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  12. Aegean

    Aegean Junior Member

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    You should load test your 12v battery for free at any Toyota dealership or parts stores like Autozone, advance auto or Pepboys. Luckily for you there is $40 off plus 25% on AGM batteries on PepBoys bringing it just to $125 including installation. Make sure they install the vent. Or pay $300 at the dealer.

    One thing that is very important for the Prius 12v battery is that it can and it will degrade the hybrid battery the last 3-6 months if you wait until it fails completely. Since there is no starter like other cars to warn you you will notice it is bad very late. I load test my battery on my hybrids when the 12v battery becomes 5 years old and with every oil change after that and I replace it immediately with first weak test. Some hybrid battery rebuilders void the hybrid battery warranty if your 12v battery is weak and strongly recommend to change it at 5 years.
    I personally changed one at 8 years and another one at 6 when the CCA test showed weakness.
     
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  13. sam spade 2

    sam spade 2 Senior Member

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    One thing even more important is that you not believe everything that you see posted on the Internet.
    Where exactly did you get that load of bull from ??
     
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  14. Aegean

    Aegean Junior Member

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    Proof is that many hybrid battery rebuilders void their warranty if your 12v battery is weak or bad. A weak 12v battery needs constant charging overloading the hybrid battery so much that can degrade it if this continues to happen for many months.
    At doctor Prius we offer prices based on Warranty
     
  15. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    It sounds plausible, that an ailing 12 volt battery might overtax the hybrid battery.
     
  16. sam spade 2

    sam spade 2 Senior Member

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    Using that logic, I guess that one should never run your air conditioner either.
    I'm pretty sure that it draws a lot more power than a moderately weak 12 V battery.

    If your 12 V is really sick, I think there would be other symptoms WAY before it strains the HV battery.

    And finally, companies very often look for lame excuses to void their warranties.
    This might just be another one of them.
    I wonder if the Moss-Magnuson act would apply in this kind of situation ?

    Just guessing here.......but I bet that NO company has the provision in their warranty if they sell new batteries or ones rebuilt with all new cells.
     
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  17. dolj

    dolj Senior Member

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    That should actually be a big red flag. If their batteries are that weak to start with, that a moderately weak 12 V battery would tip it over the edge, you should turn and run away from that deal. Run as fast as you can!


    On another note, I sense a disturbance in the Force, as I find myself strangely agreeing with SS2's last two posts. Wonders will never cease.
     
  18. cyberpriusII

    cyberpriusII Prodigyplace says I'm Super Kris

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    So, this post got me all stirred up and I dutifully trekked out to the tool shed and rooted around until I found my multi-tester (which I shamefully threw in a random box a couple of months ago after a household wiring problem gone bad...Household electrical outlet question | PriusChat)

    I then looked up information passed along to me by a member whom I have not seen about lately -- UART -- which told me how to use the tester to check the 12v.

    After having not been driven since about 7 p.m. last night, at 8 a.m. this morning, checked the voltage at the underhood jump point -- it read 12.3v solid -- I also checked our Subaru, which had also sat more than 12 hours and it read 12.38v,

    Subaru battery has been in service for about four months, but they are well known to put in really marginal OEM batteries straight from the factory.

    The Prius battery is a GS YUASA TrueStart, made in Japan in June 2013 and installed by myself in January 2014.

    Think I will live a bit dangerously and will rely on it to get through the upcoming winter....if not...what's the worst that can happen! :whistle::whistle::whistle::whistle:

    Kris (I just love replacing batteries in sub-freezing temperatures as I did in 2014).
     
  19. sugar land dave

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    Being 20 miles from home, out in the country with few people around to jump start you, can make you better appreciate a preventative maintenance procedure. I got lucky with a guy who had jumper cables. Now I have this:

    IMG_20190907_180537.jpg
     
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  20. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    What am I looking at?
     
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