Are there any real advantages to a larger 12v replacement battery?

Discussion in 'Gen 3 Prius Main Forum' started by Johnny Cakes, Feb 12, 2018.

  1. Johnny Cakes

    Johnny Cakes Member

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    Since I seem to be in the market for a new battery (I'm the OP in this thread -- Battery toast?), I have been reading the "larger replacement battery" threads and even the "mobility battery" thread.

    I'm not sure what value a larger battery would have in a Prius. I certainly understand the value of a larger battery in a traditional car.

    My understanding is that the Prius 12v battery has no direct role in starting the ICE; the 12v battery is ONLY being drained during ACCESSORY mode or while in OFF mode to keep electronics memory active or for other items (dome light, headlights) that will work in OFF mode.

    Assuming no use of ACCESSORY mode, it seems as if the value of a larger battery is only whatever additional time you may get if you leave lights on while in OFF mode. If you do kill the battery, the proponents of a mobility battery indicate that it "bounces back" better.

    What am I missing?
     
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  2. Rmay635703

    Rmay635703 Active Member

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    If you like running a big amp, a ac inverter or like sitting with the car off listening to music for hours, maybe

    Otherwise besides possibly being a cheaper battery option no real advantage
     
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  3. bisco

    bisco cookie crumbler

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    the only real downside of the oem battery is its inability to recover from deep discharge.
    if you don't drain it by leaving a light on or something, it is perfectly suited for the job.
    i replaced my 2004 in 2012, my 2008 in 2018, and my 2012 is still going strong.
     
  4. Johnny Cakes

    Johnny Cakes Member

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    I got to replace the OEM and will probably go 3rd party vendor. Mostly I'm wondering whether there is any advantage to going larger capacity assuming no use of ACCESSORY mode.
     
  5. bisco

    bisco cookie crumbler

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    what do you mean by larger, optima or similar?
     
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  6. kc410

    kc410 Active Member

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    With no accessory use, there is no advantage to be gained by having a larger capacity 12V battery.
     
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  7. grid

    grid Member

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    There is one reason that I can think of that's crucial, that is if you accidentally leave a light on overnight. If you have parking lights on while engine is on and cut the engine off, the parking lights will go off also. But if you then put the car in ACC (press power button twice without pressing brake pedal down) and press power button to turn car completely off, parking lights comes back on and stays on even if car is completely off. I discovered that by accident one day at work, when work was over and back to the car, saw parking lights on. I started the car with HV battery w/6 bars and when ICE shut off in 3 minutes after cold soak HV battery had 2 bars left.

    Had the battery been ginormous, I would have not lost 4 bars.
     
  8. Johnny Cakes

    Johnny Cakes Member

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    Yep, greater reserve capacity. Obviously CCA is irrelevant for a Prius. I saw many threads about using a battery with a greater RC than the OEM battery but wasn't sure of the advantage, except for accidentally leaving lights on. Sounds like there really is no advantage other than that. I thank everyone for helping me with my due diligence on this purchase. :)
     
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  9. David Beale

    David Beale Senior Member

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    A higher A-Hr capacity battery will survive longer with the car sitting unused. It will also benefit from lower percent discharge each night. That -might- lengthen its' life. Any lead acid battery will suffer from discharges below some percent of its' capacity. If you start with a higher capacity battery you discharge less of its' capacity each night on a percent basis. For example, assume your car's parasitic load discharges the battery 2 A-Hr each night. For the stock battery this would be about 5% of capacity. If you replaced the stock battery with a 50 A-Hr one, that 2 A-Hr would be 4% of capacity. If you went on vacation and left the car at the airport for, say, 2 weeks, the stock battery would discharge about 73% whereas the 50 A-Hr one would discharge about 48%. The stock battery would suffer some damage or loss of life whereas the 50 A-Hr replacement might not.

    It gets worse. All the above assumes the battery gets fully charged when the car is driven. This is often not the case. Pearl S' battery often runs at 70% charge, maybe even less, due to short trips.

    A larger A-Hr capacity battery should therefore last longer, especially if you can find one that will allow topping up the water loss that all lead acid batteries suffer with use.

    Of course the downside is higher weight and whether or not it will fit. ;) DO get a "deep discharge" type to minimize the damage of low charge operation. As you have said, CCA has no bearing in a Prius. I know Panasonic makes very nice lead acid batteries that allow water to be added yet are well sealed. Don't know if they will accept a vent tube though. The FJ Cruiser came with one. Still using the original 2007 one in that vehicle.
     
    #9 David Beale, Feb 13, 2018
    Last edited: Feb 13, 2018
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  10. MelonPrius

    MelonPrius Member

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    I'm impressed. I hope to duplicate your results here in the desert, but I've had terrible luck with batteries in Vegas. I just replaced my Accord's battery this week and the battery installer/seller told me that Prii in my town have long lasting 12v batteries because they don't do much, by comparison. My Prius' 12v has 4 years under it's belt and I hope it makes it to 6 years.
     
  11. bisco

    bisco cookie crumbler

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    no question, heat is a killer.
     
  12. David Beale

    David Beale Senior Member

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    Yes, reality is strange. Everyone thinks cold weather is the killer for lead acid batteries.

    "It was very cold and the car wouldn't start". The battery was just fine, it just couldn't put out starting current. That is, it was fine until people started to mess with it. ;) If you just warmed it up a bit the battery would work well and not be damaged.

    It's heat that is the killer! Yes, a hot battery will start the car. For a little while. Then it will die. ;)
     
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  13. Prodigyplace

    Prodigyplace Senior Member

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    Actually too much heat or cold causes the issues. Moderation in everything. ;):D
     
  14. David Beale

    David Beale Senior Member

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    Yes, but my point is cold temporarily disables a battery, heat KILLS it. ;)
     
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  15. rrg

    rrg Member

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    I did the larger 12v battery that is mentioned in the forum here with the vent and larger OEM toyota battery clamps.
    The only advantage I noticed is the ICE would not run when going down hills or coasting on long stretches of road. I watched on my ScanGuage. So the car was actively turning off more often if the 12v had a longer lasting full charge IMO.

    My stops at the street lights were also much more quiet since the ICE did not run reguardless of accessories being used.

    FYI - Here is my test:
    Turn on the radio with the heater on and fan running about medium to high at the start of a street light.
    If the ICE turns on during the light then the battery is not strong enough to hold off the ICE with the small battery. Mine holds it off at every light all the time.

    I know there are alot of variables between everyone but try it and see.
    Then do it again with the new battery and see what happens under the same conditions.


    here is the thread.

    my2cents.
     
    #15 rrg, Feb 14, 2018 at 8:43 PM
    Last edited: Feb 14, 2018 at 9:03 PM
  16. Rmay635703

    Rmay635703 Active Member

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    CHEAPER!

    That is the only reason
     
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  17. padroo

    padroo Senior Member

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    All computers have a minimum voltage they will operate at, when the voltage is above this amount they are happy. The Prius is a computer on wheels, If you can't maintain propper voltage the Prius starts acting strange.
    This winter is proof of what low voltage is all about.
     
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  18. qdllc

    qdllc Senior Member

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    Not much help, but if I wasn’t looking to run stuff off the 12v battery, my focus would be on getting a quality battery.

    As a comparison, my current motorcycle battery is a sealed AGM model that was highly recommended. So far, it’s held up longer and more reliably than the traditional OEM design. Well worth the extra I paid for it.
     
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  19. padroo

    padroo Senior Member

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    The AGM battery takes vibrations better than a conventional battery, this is one big advantage.
     
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  20. David Beale

    David Beale Senior Member

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