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Has anyone tried replacing the 12 volt battery with a LiFePO4 12.8 V battery?

Discussion in 'Gen 4 Prius Technical Discussion' started by GoodOldBob, Dec 1, 2023.

  1. GoodOldBob

    GoodOldBob Junior Member

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    I am interested in substituting a 50 or 100 AH 12.8 Volt LiFePO4 (LFP) to replace the Lead Acid battery. Mainly for the increased storage capacity and increased cycle life. Has anyone tried it yet? Did it work OK? Please let me know if you have done it.

    --GoodOldBob
     
  2. sylvaing

    sylvaing Active Member

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    Does that battery has its own heater to allow it to charge below freezing? Charging a frozen Lithium battery will damage it.
     
  3. GoodOldBob

    GoodOldBob Junior Member

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    Most quality LFP battery management systems include a low temperature cutout that blocks charging when too cold. Remember that the engine bay of the Prius doesn't stay below freezing for very long after the engine kicks in.
     
  4. bisco

    bisco cookie crumbler

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    Pretty sure this has been done multiple times, search google with Prius chat
     
  5. sylvaing

    sylvaing Active Member

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    Oh, right. The engine in the standard Prius is used quite often. I guess that could be different in a Prime.
     
  6. Doug McC

    Doug McC Active Member

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    You may want to investigate the charging requirements for each of the batteries. The charging algorithms for a lithium battery are significantly different than those of a lead acid battery. A starting point might be The Battery University (yep, it actually exists). Or, you could just rely on the opinions of folks who don’t even know there are significant differences between the two (like PC egineers (misspelling intentional) ;)
     
  7. Me_

    Me_ Junior Member

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    That question has been answered. Do a google search.

    In short due to a difference in the resistance between a standard 12v car battery and a lithium-ferric 12 v battery, you will burn the alternator; seriously burn it..
     
  8. sylvaing

    sylvaing Active Member

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    Good thing the Prius doesn't have an alternator then ;)
     
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  9. SWHPBT

    SWHPBT New Member

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    My understanding is the Prius 12V battery is charged via a DC-DC converter from the hybrid battery and there is no 12V alternator in a Prius.
     
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  10. sylvaing

    sylvaing Active Member

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    Your understanding is correct.
     
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  11. GoodOldBob

    GoodOldBob Junior Member

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    Which is why I ignored the reply left by "junior member" ME_ . I assumed he/she/it wasn't fully appraised of the facts about the Prius electrical system. Thanks for making them aware.

    GoodOldBob
     
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  12. Robert21PrimeLTD

    Robert21PrimeLTD New Member

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    What about a AGM (absorbent glass mat) battery? Would that be okay?
     
  13. Doug McC

    Doug McC Active Member

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    Not in a 2020 (contrary to what some will tell you here). One, the charging algorithms were set up for lead-acid (meaning you will shorten the life of the AGM); Two, you won’t REALLY gain anything; Three, you will waste your money; Four, there is a slight (emphasis on “slight”) chance of damaging the ECU system (it’s assuming you are smart enough to read the owner’s manual and not to replace the battery with the wrong type).
     
  14. GoodOldBob

    GoodOldBob Junior Member

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    My original idea is to have a car that is totally free from ancient lead-acid technology and all it's drawbacks. Even if the charging algorithm isn't optimal, a less-than 100% charge would be fine and not shorten the LiFePO4 cycle life of 3000 to 4000 full charge/discharge cycles. And with that kind of performance, the 12 Volt battery could be expected to outlast the HV traction battery.
     
  15. Robert21PrimeLTD

    Robert21PrimeLTD New Member

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    My AGM question is because my sister, who has a non-plugin Prius, had her 12v battery die during Covid lockdown and had to get a jump start and then drive around while braking to charge the 12v. Is my plugin different? Will plugging in the HV battery charge or help the 12v battery? I'm new to hybrid technology and am not sure of how the charging systems work.
     
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  16. GoodOldBob

    GoodOldBob Junior Member

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    I'm told the plugin Prius charges both the HV Traction battery and the 12 Volt Accessory battery when plugged in and charging.
     
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  17. sylvaing

    sylvaing Active Member

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    Yes, your plugin will charge the 12V battery at a voltage of 12.8V while charging. It will also charge the 12V battery at a voltage of 13.5V when plugged in, not charging and the heater elements are actively heating the battery pack because it got below 2°C.
     
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  18. vvillovv

    vvillovv Senior Member

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    Are both those voltages consistent for the span of times for both charging and battery heater warming the pack?
    And if you ever use pre-conditioning and monitor the 12 volt batteries voltage, do you also see a similar charge rate during that 10 minute session?

    I'm sure you've noticed all the complaints about how the Gen 4 and 5 plug-ins don't charge the 12 volt battery at all while plugged in and only charge that 12 volt battery while in Ready Mode. and that rumor spreads pretty fast. Possibly due to the cars may not always charging the 12 volt battery when some owners take a look at their 12 volt battery voltage one time and think they've discovered a big problem. Than start looking for the parasitic draw which keeps the 12 volt battery at their observed SOC.

    My 12 volts SOC is typically around 12.2 volts, until I post that stat here and than next time I look the voltage is around 12.5 ... lol
     
    #18 vvillovv, Mar 24, 2024
    Last edited: Mar 24, 2024
  19. RandyPete

    RandyPete Member

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    SOC is a power rating in percent of the battery watt-hour rating. It is not the voltage of the battery.
    Watt-hour=VoltXAmp-hour
    A 12 volt 100 amp-hour battery is a 1200 watt-hour battery (12Vx100Amp-Hour battery rating = 1200Watt-hour battery capacity)
     
    #19 RandyPete, Mar 24, 2024
    Last edited: Mar 24, 2024
  20. vvillovv

    vvillovv Senior Member

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    What are you trying to say?
    Is your post supposed to have something to do with the question I asked @sylvaing about his 12 volt battery readings?