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Trying to put battery tender on my 12V battery....Positive post plastic cover?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ualdriver, Nov 3, 2013.

  1. ualdriver

    ualdriver Member

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    I tried to start my 2008 Prius today and I got a literal Christmas tree of lights, red exclamation mark, one headlight sort of on, one off, etc., so I am assuming that my 5 1/2 year old 12V battery is dying. I also haven't driven the car in a couple of days and the temp has been dipping into the low 40's lately, so I'm assuming it's time for it to get replaced.

    I want to put a 12V battery tender on the battery so that I am sure it will start tomorrow, but the positive post of the battery has the large, plastic, red/black cover thing on it. How do you take it off? I couldn't find anything in the manual. I'm not sure if it pulls off or if there are snaps I have to depress, but it looks like cheap plastic and I don't want to break it.

    Could someone tell me how it comes off??? Thanks!
     
    #1 ualdriver, Nov 3, 2013
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    It is not really necessary to remove the red cover. Just bend the cover up enough to gain access to the positive battery terminal. Make sure all the passenger cabin and hatch lights are turned off to minimize power being lost to non-charging activities.

    Or, remove the lid on the main relay/fuse box near the inverter, pivot the red cover for the dedicated jumpstart terminal up, and use that as the positive battery terminal.

    A battery tender typically will produce around 1A or 1.5A, so don't expect much from that if your 12V battery is seriously depleted. If you run the battery tender for 8 hours continuously, you might get 8-12Ah while the battery capacity is around 40Ah. Also, some power is lost to heating the battery. So, the car might start or might not, tomorrow.

    Better to use a battery charger which produces much more charging current. If that is not available, then the tender is better than nothing - just allow as much time as possible for the charging process, and you may have to use the tender over several days to get the battery back up to full charge, depending upon its current discharge condition and whether it will even accept a full charge.
     
    #2 Patrick Wong, Nov 3, 2013
  3. ualdriver

    ualdriver Member

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    Thanks Patrick, as usual, for your advice.

    The car would not start when I had the headlights on. That's what gave me the Christmas Tree of lights. But when I turned the headlights off, the car started. I drove it around for 15 minutes or so and it appeared to be good. I just want to make sure that when I wake up at o-dark-early tomorrow that the car starts so I can take it to the dealership to get the new battery installed.

    **But just to be sure, it's OK to put the battery tender cables directly on the posts of the battery without disconnecting the battery completely from the car first?
     
    #3 ualdriver, Nov 3, 2013
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  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    15 minutes is certainly not enough time to make any difference on the 12V battery state-of-charge.

    Yes, it is OK to connect the battery tender cables on the battery without disconnecting the battery from the car, AS LONG as you correctly connect the polarity.
     
    #4 Patrick Wong, Nov 3, 2013
  5. ualdriver

    ualdriver Member

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    Yikes! I thought (incorrectly I guess) that if I was out driving about that the ICE would run until the 12V was fully charged. How long should I drive the car to make sure that the 12V battery is fully charged so it will start in the morning? My tender doesn't put out much electricity, as you correctly surmised.
     
    #5 ualdriver, Nov 3, 2013
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Your best bet would be just to leave the Prius READY overnight, assuming you have sufficient fuel in the tank.
     
    #6 Patrick Wong, Nov 3, 2013
  7. ualdriver

    ualdriver Member

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    thanks again Patrick...remind me to buy you a beer or two if we ever meet :)
     
    #7 ualdriver, Nov 4, 2013
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