1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Can Gen1 drive 100 miles w/ bad 12v battery?

Discussion in 'Generation 1 Prius Discussion' started by Raqune, Jul 6, 2014.

  1. Raqune

    Raqune Junior Member

    Joined:
    Oct 8, 2008
    28
    12
    0
    Location:
    Portland Oregon
    Vehicle:
    2005 Prius
    Model:
    N/A
    If I were stranded out of town with failed 12v battery on a Gen 1 prius, could I jump start it and drive 100 miles or so without further damage to car?

    In the "old days" one could jump start a car and drive it with no battery, just depending on the alternator to support system needs - I know the Prius is a long shot from the "old days" and even some non-hybrid cars can't do this anymore but I was curious how this might affect the Prius.
     
    #1 Raqune, Jul 6, 2014
  2. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,134
    15,394
    0
    Location:
    Huntsville AL
    Vehicle:
    2018 Tesla Model 3
    Model:
    Prime Plus
    The bottom of the power inverter has a traction-battery to 12V inverter or actually 13.9V. If the 12V battery went bad because the 12V inverter failed, you won't be going far. But a series of fully charged, 12V batteries can be used.

    GOOD LUCK!
    Bob Wilson
     
    #2 bwilson4web, Jul 6, 2014
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,134
    15,394
    0
    Location:
    Huntsville AL
    Vehicle:
    2018 Tesla Model 3
    Model:
    Prime Plus
    Take care not to reverse the polarity or you can destroy the 12V inverter.

    Bob Wilson
     
    #3 bwilson4web, Jul 6, 2014
  4. Raqune

    Raqune Junior Member

    Joined:
    Oct 8, 2008
    28
    12
    0
    Location:
    Portland Oregon
    Vehicle:
    2005 Prius
    Model:
    N/A
    I was thinking more in terms of an age related failure. Inverter & HV battery all working, just the 12v say had a shorted or open cell or something so the voltage was wrong. Could the car drive once booted up, or would this damage something because it would try to make the voltage right until it self-destructed.
     
    #4 Raqune, Jul 7, 2014
  5. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,134
    15,394
    0
    Location:
    Huntsville AL
    Vehicle:
    2018 Tesla Model 3
    Model:
    Prime Plus
    I've measured a maximum current load of ~75A, a little over 1kW. So if the 12V has a shorted cell, it could get pretty hot and boil off what remaining electrolyte exists. I would not recommend it.

    A small, cheap, lawn tractor or mower battery might be a better solution. At least it would not overheat.

    Bob Wilson
     
    #5 bwilson4web, Jul 7, 2014
  6. Raqune

    Raqune Junior Member

    Joined:
    Oct 8, 2008
    28
    12
    0
    Location:
    Portland Oregon
    Vehicle:
    2005 Prius
    Model:
    N/A
    ...and if one were to just disconnect the 12v battery after booting up?
     
    #6 Raqune, Jul 7, 2014
  7. messenger

    messenger Junior Member

    Joined:
    May 18, 2014
    30
    1
    0
    Location:
    Fairfield, IA USA
    Vehicle:
    2014 Prius
    Model:
    Three
    If you search the forum you'll find all kinds of problems associated with driving with a bad or dying 12v battery, it's a cheap fix so way risk it ?
     
    #7 messenger, Jul 7, 2014
  8. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,307
    15,098
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    As long as the DC/DC converter isn't faulty, a Prius will run quite happily this way. With older cars it was never recommended to disconnect the battery while the engine ran, because the old way of regulating voltage with a vibrating reed regulator depended on the battery being part of the story. But the Prius DC/DC converter is totally electronically regulated and will give you a rock-solid 13.8 volts or so, battery in or out of the circuit. Naturally, if you don't remember to reconnect the battery before turning the key off, you'll lose your radio presets and such. :)

    The fastest, easiest way to disconnect the battery is to squeeze and pull out the cable connector that plugs into the fuse assembly on the positive battery terminal. To reconnect, just plug it back in. Much faster than fussing with the terminal clamps.

    This is also what I do if somebody asks me for a jump. Directly jumping another car from a Prius is risky, because the other car's starting current will be higher than the fuse ratings in the DC/DC circuit and the fuses are a pain to replace. Instead, I just start the Prius first, then unplug the battery cable, then run jumper cables between my battery and the other car's. That way, I'm only using my battery as a jump source, not my battery-plus-whole-car. Once the other car's started, I unhook the jumper cables, plug my positive cable back in, and drive away. (Starting the Prius first just saves me from worrying about whether there'll be enough left in my battery after the jump attempt.)

    -Chap
     
    #8 ChapmanF, Jul 7, 2014
    Raqune likes this.
(You must log in or sign up to post here.)