Dead 12V, dead fob and AAA restart does not work

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by MICHAEL RUBY, Jan 24, 2022.

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  1. MICHAEL RUBY

    MICHAEL RUBY Junior Member

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    Location:
    Seattle WA
    Vehicle:
    2018 Prius c
    Model:
    III
    Because of the pandemic we are hardly ever driving our car (2018 Prius C). When we do it might be only to pick up groceries a few blocks away. It seems there is some sort of electronics running even when the car is turned off, so the 12V battery slowly dies. The battery was new as of March 2020. Today the fob didn't open the car so I used the little pop out key to open the door. We had AAA come out to give the battery a jump start. He told me that I did not need to do anything extra, that with his jump start it would continue to charge the 12V from the high voltage traction battery after the engine automatically shut down. That seems to have been wrong.

    The fob does not work when the 12V is dead but when he got the motor running I found that the fob still did not work. The dashboard showed that key was not in the car so you could not engage the transmission. When the engine shut down, it went dead and I had to lock the car using the little key.

    Am I going to need to have the car towed out to the Toyota dealer to deal with this? Is there anything else I can do so that once AAA gooses the battery and the engine starts running I can get the transmission engaged and I can drive it out to the dealer?
     
    #1 MICHAEL RUBY, Jan 24, 2022
  2. PriusCamper

    PriusCamper Senior Member

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    Buy a 12v battery charger...
     
    #2 PriusCamper, Jan 24, 2022
    roadrunner likes this.
  3. bisco

    bisco cookie crumbler

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    ...and a bicycle
     
    #3 bisco, Jan 24, 2022
  4. patcoghm

    patcoghm Junior Member

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    12v dead battery is a design problem. It should be if the car is plugged into power for the Drive battery charging, have it charge both batteries at the same time or one or the other. Basically add a trickle charger to charge the 12v if its below a specific voltage and the car is plugged in. I'm tired of this dead battery problem and that is one solution, or as I'm thinking to buy a trickle charger. This one is for AGM batteries like in the Prius.

    Snap-on Store
     
    #4 patcoghm, Jan 24, 2022
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    The AAA guy wasn't completely wrong- just incomplete (which is sort of partially wrong).

    Yes, once he "jump started" the car, the hybrid system inverter (DC converter) would produce power to run the car's systems and charge the battery. But only for as long as the car is turned on - aka in Ready mode. The thing is that a healthy but discharged 12V battery can take 6-12 hours to recharge. And the condition of the 12V battery has no real affect on whether the gas engine runs or not. The charge level of the HV battery determines when the engine fires up when stationary.

    So, the 12V should have a "smart" charger (compatible with AGM batteries) connected at least overnight, then have it tested at a shop (some chain auto parts stores will test). If it's old enough or was discharged long enough or too many times, it might need replacement.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, Jan 24, 2022
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  6. sam spade 2

    sam spade 2 Senior Member

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    This is a C model. There is no "plug in". ;)
     
    #6 sam spade 2, Jan 25, 2022
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