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What happens when the battery is dead?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by echase, Feb 28, 2010.

  1. echase

    echase New Member

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    The little battery, that is.

    My spouse has a tendency to leave doors open, and our small child likes to play with the dome lights, SO I just had my second opportunity to jump start our '08.

    As happened on the first time the car reported a "problem with the transmission" after power up. Putting it in gear, (out of park) and back seemed to resolve the issue, but this time the red triangle stayed lit on the dash. Rebooting did not resolve the issue, until I drove my wife to her appointment five minutes away, and rebooted when I got home.

    I left the car in the on position, in park for now... I figure an hour or so should be sufficient to recharge the low-voltage battery.

    So, my questions are:

    1. What happens to the car (in technical terms, please) when the LV battery has been exhausted. Is data lost, are there things that need to reset/recalibrate, etc?

    2. Why the "transmission error"

    3. What was the deal with the red triangle... was that likely due to low voltage readings from the 12v battery? Can I confirm this myself, or access error logs somehow?

    4. How much have I damaged my battery? I doubt the LV battery is designed to be deep-cycled... and I doubt the electronics is on any kind of relay to cuttoff below a certain voltage, so I've probably deep-cycled twice (dome lights were DEAD... no glow at all). How many more times before I have to replace the LV battery?

    Thanks for any knowledge you can share!
     
    #1 echase, Feb 28, 2010
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Depending upon how deeply discharged the 12V battery was, one hour in READY would not be enough. 8+ hours would be better, so if you have access to a battery charger (using the 2A position) it would be well to set that up.

    Answers to your questions:

    1. You will need to reset the driver's window auto up/down. The radio station presets may be lost. The trip odometer probably will be reset to zero and the fuel gauge will show a blinking one bar until the system determines how much fuel is in the tank.

    2. A glitch, don't worry about that.

    3. Yes, most likely due to the battery. Don't worry about DTC if you don't have any other problems.

    4. Who knows. If the battery doesn't hold a charge after you've allowed sufficient time for a recharge (see my comment above) then you'll need to replace it. Good luck.
     
    #2 Patrick Wong, Feb 28, 2010
  3. richard schumacher

    richard schumacher shortbus driver

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    You can prevent these problems by always locking the car when you park it. Umm, that is, if you can persuade your spouse to do so also... feedback is useful: require the person who left it unlocked to get it jumped :_>

    Low voltage can confuse the hell out of computers and their memories, so almost any weirdo symptom is not surprising.

    Draining the battery has certainly reduced its life by some amount. You can test it yourself without tools using the procedure given here:
    http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html
     
    #3 richard schumacher, Feb 28, 2010
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