How smart is in-vehicle system?

Discussion in 'Prime Main Forum (2017-2022)' started by jharris378, Nov 23, 2025 at 2:44 PM.

  1. jharris378

    jharris378 Junior Member

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    Can the in-vehicle system charge a low voltage battery?

    I’m certain my battery voltage is low because I haven’t charged or driven my car for months. I’ve been in the hospital and rehab. I haven’t been able to open the charge door because the 12V battery was dead.

    if I replace the 12V battery so I can open the charge door, will the primary battery charge if I plug it in?
     
  2. ForestBeekeeper

    ForestBeekeeper Active Member

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    When you plugin to charge your drive battery, that does not charge your 12vdc starting and accessories battery.
     
  3. otatrant

    otatrant Active Member

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    You can jump start the car and run the car to charge the auxiliary or trickle charge the 12V auxiliary battery. You need to have a charged 12V auxiliary battery to charge the big traction battery. The 12V auxiliary battery runs a system that monitors the charging of the big traction battery.
     
  4. BiomedO1

    BiomedO1 Senior Member

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    Sorry, a bit confused here. I didn't know there was a 2006 PHEV.
    When you say 'battery door' do you mean your car door? Assuming you have a PHEV, there is NO lock on the charge port door. There is a charger handle lock on the higher end PHEV, but not on the basic.
    No; it won't revive a dead battery. ONLY while the traction battery is actively charging, the 12V system is turned-on to ensure power to the cooling fans and activate ECU's required to perform this tasks. The 12V battery will receive some power, but it won't be enough to revive a nearly dead battery. That battery will need to be fully recharged and tested to verify that it wasn't damaged from the deep discharge.
    Same goes for jump-starting the car and driving it around for a half hour. This system isn't designed to bring a dead 12V battery back to life and you still need to verify that the battery wasn't damaged from the deep discharge. An ICE car is always pumping 14+VDC into the battery while the ICE is running, the Prius is bias towards sending most electricity generated back to the traction battery to extend the cars range and lower gas consumption - so 'old-wives tales' don't work here, it's a different beast altogether.

    There's a jump-point under the hood to jump-start the car - that's where you can attach a jump pack or battery charger. To get into the car, your FOB has a hidden manual key - that should be able to open your drivers' door. Again; I'm making assumptions here; because if you don't have the original OEM FOB and lock set; that back-up key isn't going to work. Any FOB can be programmed to unlock and start your car - but if the locksmith didn't go the extra mile to 'recut' your manual back-up keys - your SOL.

    Hope this helps......
     
    #4 BiomedO1, Nov 23, 2025 at 4:29 PM
    Last edited: Nov 23, 2025 at 4:52 PM
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  5. jharris378

    jharris378 Junior Member

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    I didn’t get my question across well. First, it’s a 2019 plug-in Prius with a dead 12V battery (original battery). So, the 12V battery needs replacement.

    However, with the dead 12-V battery, I haven’t been able to open the charge port door to plug it it. Once I replace the 12V battery I can plug in the type 1 (110 VAC) charger I use.

    my question is if the car’s software is smart enough to charge the primary battery if it’s voltage has fallen too low (I presume it’s a lot less than 20% SOC -whatever that voltage is). The primary battery hasn’t been charged for over six months.

    The car may need a primary battery (high voltage) trickle charge only available at the dealer. I’m hoping the car’s charging software will allow it to charge even the primary battery voltage is low. I don’t know but I’ll try unless told not to by someone who has experienced the same thing.

    I was just hoping someone here might know ahead of time.
     
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  6. BiomedO1

    BiomedO1 Senior Member

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    Thank You; In the future; please mention which car your talking about or change your profile to reflect the correct car.

    I wasn't aware you needed power to open the charging port door on a PHEV. That would be the passenger side fuel door. The driver's side fuel door (gas) requires power to open. You do need power to open the gas door on that car - at least on a 2021 that charge door just pops open with a push - spring loaded. Push on the REAR facing side of the charge port door; if your confused.
    The traction battery software is smart enough to take care of itself. Once you plug it in; it should recharge without an issue. The car's ICE system may stumble a bit, because it has lost all of it's learned presets. You can first try recharging the battery under the hood. After it's fully charged, drive over to the nearest parts supplier to get the battery tested. If your feeling flush - just replace it - $200 down the tubes.... There really isn't a need for dealership intervention - that dealership trickle charge is nonsense. You've got a PHEV, plug it in yourself. If it wasn't a PHEV, trickle charging may be required - but that wouldn't stop an unscrupulous dealership form charging you for that. This wouldn't be the first or last time a dealership charged someone for something they didn't need......

    I know a few people that has NEVER plugged-in their PHEV - they all run fine.......

    Good Luck.
     
    #6 BiomedO1, Nov 23, 2025 at 7:19 PM
    Last edited: Nov 23, 2025 at 7:42 PM
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