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12V battery ran down... some tips

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by wfolta, Nov 22, 2010.

  1. wfolta

    wfolta Active Member

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    1. You CAN leave your headlights on. If you turn them on (or off and back on) after the car is turned off, you override the auto-off feature and it doesn't appear to have a fail-safe. This is bad.

    2. If the 12V is really low, there won't be enough power to unlock the hatchback, which seems to take more power than the doors. You can, of course, open the driver's door with the emergency key, then crawl/reach into the back.

    3. You have to lift the back-center storage tray up to free the back-passenger-side 12V compartment. It's all a little awkward from inside the car, and you might want to familiarize yourself with the locations of things.

    You may want to do all of the moving of stuff yourself, with the doors closed, to preserve 12V power, since the overhead lights will be on as long as the doors are open, and they do run the battery farther down.

    4. I called AAA and they sent out a guy to help. He insisted on testing the battery before applying power and his tester indicated that the battery should be replaced. I believe the tester was wrong, though, mislead by the 12V's low amperage (no need to crank the engine, so it's much smaller than most 12V's). Not sure about this, but I've seen no indication since that the battery actually needs replacing. So don't just replace the battery because the tech says so: do your own investigation. I'd appreciate clarification on this.

    5. The tech had a handheld battery-booster kind of thing and the instant he hooked it up, the interior lights came up full and the car was able to go to READY. I don't think you need to keep external power applied after this: I think once the traction battery's online you're good to go. I'd appreciate any clarification on that.
     
    #1 wfolta, Nov 22, 2010
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    4. Yes, if the 12V battery holds a charge and you don't have further no-start problems then there is no reason to buy a new battery.

    5. Once the Prius is READY, you can disconnect "external power". For that matter you could disconnect the internal 12V battery. Of course, with the 12V battery disconnected, once you make the car IG-OFF you won't be able to make it READY again.
     
    #2 Patrick Wong, Nov 22, 2010
  3. macman408

    macman408 Electron Guidance Counselor

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    In addition to the correct comments above:
    1. It's not bad, it's by design. If you turn your headlights on after the car is off, it's assumed that you want them on. I suppose they could've made some low-voltage-triggered auto-off too, but it'd be hard to engineer it such that the set voltage would always allow the car to be started yet wouldn't turn the headlights off too soon.

    2. It's not that the hatchback takes *more* power, it's that it takes *any* power. The hatchback latch is electronic, the other doors are purely mechanical. There is an emergency release lever in the hatchback door, but it's tiny, hidden, and hard to get to and use.
     
    #3 macman408, Nov 23, 2010
  4. tumbleweed

    tumbleweed Senior Member

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    3. It would be easier to use the under hood jumper terminal.

    4. The tester he had can't really determine if the battery is bad or not, you should charge it up and keep using it. If it goes dead again for no reason then you need to check out the car (charging system and current draw when off) and the battery. A battery shop should be able to do a test discharge on the battery which will tell you it's capacity, this should take several hours if done correctly and is the best indication of it's condition.
     
    #4 tumbleweed, Nov 23, 2010
  5. Troyroy

    Troyroy Member

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    #5 Troyroy, Jan 10, 2011
  6. oldfridayrider

    oldfridayrider Junior Member

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    You don't need to access the 12V battery use the terminal in the fuse box(+) and the engine for - and it should power up. Extension cord size wire will do.
     
    #6 oldfridayrider, Jan 10, 2011
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