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12 Volt Auxiliary Battery + Cold Weather

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by jsndyr, Jan 18, 2011.

  1. jsndyr

    jsndyr New Member

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    Newbie here... I've looked through the forum for an answer to this question, but I'm not finding anything specific to what I am looking for.

    I have a 2007 Prius that recently required a replacement of the 12V battery. I frequently travel and the Prius sits for 4-6 days at a time at the airport. My Prius was dead when I returned from my last trip (4 days, really cold weather). I had it jumpstarted and drove it home (50 miles). The next morning it was nearly dead again (turned on some of the electronics, but not all). The battery was obviously dead. So I replaced it with a Toyota battery and all seems well again. I do have questions though.

    I have been periodically checking the battery to see if I am getting any sort of drain as I am paranoid about being stranded at the airport again. I have a six day trip coming up and I don't want to come back to a dead car... again.

    Here is what I have tracked for the past four days:
    Saturday -- 12.56V (garage temp = 25)
    Sunday -- 12.55V (garage temp - 20)
    Monday -- 12.56V (garage temp - 36)
    Tuesday -- 12.53V (garage temp - 27)

    I have the smart key system (SKS) turned off at this time.

    I read somewhere on the forum that temperature affects the voltage of the battery (fully charged at 0F is not 12.6). Do these voltages look right considering the age of the battery and the temperature in the garage? Should I be looking at anything else?

    Thanks for listening!
     
    #1 jsndyr, Jan 18, 2011
  2. qbee42

    qbee42 My other car is a boat

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    How are you checking the battery? Those voltages are a little low for an unloaded fully charged battery, but not bad for a cold Prius battery supplying quiescent loads.

    Tom
     
    #2 qbee42, Jan 18, 2011
  3. jsndyr

    jsndyr New Member

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    I was testing with a multimeter on the jump point found in the engine compartment with nothing running (no aux power, just cold battery). I just checked directly on the battery and showed 12.56V.
     
    #3 jsndyr, Jan 18, 2011
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I suggest that you purchase a battery charger and use that to fully-charge the battery prior to your business trips, as well as every two weeks as a maintenance practice. 12.56V when IG-OFF isn't bad, but a fully-charged AGM battery will be closer to 12.9V.
     
    #4 Patrick Wong, Jan 18, 2011
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  5. fotomoto

    fotomoto Senior Member

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    Just curious, why don't you use a taxi instead of multi-day parking charges?
     
    #5 fotomoto, Jan 18, 2011
  6. MJFrog

    MJFrog Active Member

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    I believe the OP said (implied) 50 miles one-way to the airport.
     
    #6 MJFrog, Jan 18, 2011
  7. jsndyr

    jsndyr New Member

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    I live a good distance from the airport (50 miles). The cost of parking is still cheaper than taking a taxi and most shuttle services operate within a 25 or 30 mile radius of the airport and those that do service my area cost double what it does to park at the ramp. Ideally, I'd simply use the train, but its schedule doesn't align with my typical travel times.
     
    #7 jsndyr, Jan 18, 2011
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    Doesn't the second gen have an under-dash button to disable constant searching for a smart key or something? Maybe that is is significant enough over 4~6 days.
     
    #8 Mendel Leisk, Jan 18, 2011
  9. jsndyr

    jsndyr New Member

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    Patrick, thanks for the tip. I am going to pick up a battery tender today to give that a try. The charge has held pretty steady around 12.55, so I'm not too worried about something putting a drain on the system at this time. Are the Deltran tenders any good?
     
    #9 jsndyr, Jan 18, 2011
  10. jsndyr

    jsndyr New Member

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    Yes, there is a button for the SKS. I have disabled it for the time being as I read that could have been part of the initial battery drain problem.
     
    #10 jsndyr, Jan 18, 2011
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