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Prius Battery Drain

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Nathan James Byrd, Apr 26, 2019.

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  1. Nathan James Byrd

    Nathan James Byrd Junior Member

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    2007 Prius
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    Hello,

    I have a 2007 Prius with 137K miles on it that I bought about a year ago. From the beginning it has had issues where if I didn’t drive the Prius for about a week it would die and I would have to have someone jumpstart it. I took it to Toyota and they fixed a door handle and replaced the 12 volt but that didn’t work. Then I took it to them a second time and my hybrid battery failed so I replaced that. However, my Prius is will still die if I leave it without driving for 5 days or more. Any ideas what this might be? Any help is appreciated I can’t really afford to take it to Toyota again!
     
    #1 Nathan James Byrd, Apr 26, 2019
  2. JC91006

    JC91006 Senior Member

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    When you got the new 12v battery, was it charged at any point? Did the dealer charge the battery when you brought it back to them the 2nd time?

    There may also be 3rd party electronics that were installed and draining the battery. An aftermarket alarm would normally do it
     
    #2 JC91006, Apr 26, 2019
    Raytheeagle likes this.
  3. exstudent

    exstudent Senior Member

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    1) As JC says, maybe the installed 12V was not fully recharged before installation?
    2) Maybe the the installed 12V is defective?
    3) Maybe the map light was left ON, over those 5 days? That could drain the 12V enough to possibly need a jump.

    I suggest you get a smart 12V battery charger that is AGM compatible. Here are some suggestions.
    $73 Schumacher SSC-1500A-CA
    $85 CTEK MUS 4.3
    $60 NOCO Genius G3500

    How long (durration/distance) do you drive each work day (assuming 5 days a week, M-F)? If you have a short commute (say <15min), this might NOT be long enough to help to keep the 12V battery fully charged. The Gen2 Prius 12V bus has a low amperage recharge rate, thus the need for longer drive durations or the owner to periodically top off the 12V by recharging at home. Toyota did not make this mistake w/ the Gen3 Prius, as the 12V bus has a much heftier amperage recharge rate.

    Do you listen to the radio in ACC or IG-ON, for prolonged periods? ACC would be a better position to listen than IG-ON. But, doing either, esp IG-ON, repeatedly for prolonged periods will drain the 12V battery.

    If you still are at a loss contact Matt at Texas Prius Battery Replacement
    He is in the DFW area.
     
    #3 exstudent, Apr 27, 2019
    Last edited: Apr 27, 2019
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  4. TMR-JWAP

    TMR-JWAP Senior Member

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    One item that can cause a drain on the 12v battery while the car is off, is the (B18) Brake Control Power Supply. This is the black box located just to the driverside of the 12v battery. This box has 28 capacitors which store energy as a backup for the brake system in case there is a loss of main power. Failures in this box can result in an abnormal drain and kill the 12v battery relatively quickly when the car is off. The BCPS is powered directly from the 15 amp ABS MAIN 3 fuse located in the engine compartment fuse compartment.

    Also just noticed that the BCPS provides power to the driver Door Courtesy switch. Perhaps this switch is stuck?
     
    #4 TMR-JWAP, Apr 27, 2019
    Last edited: Apr 27, 2019
    JC91006 and SFO like this.
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