12 volt battery loose connection

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by chocolatemint, May 21, 2021.

  1. chocolatemint

    chocolatemint Junior Member

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    Hi. I have a 2004 Prius I bought and have driven more than 230,000 miles. I put in a new 12 volt battery last year myself (which may be the problem). It has functioned well until about a month ago when I would often try to start the car and find no electricity. No door locks. No light. I thought it was the battery itself, but I found that if I pounded on the battery cover (as you know its located in the right back corner of the trunk), voila, the electricity would engage, and I'd be a happy camper. The linkage to the battery would continue to disconnect for weeks, and I just banged on the cover, and voila. Finally, I had my friend, a Toyota engineer from the original generation 1 and 2 design team in Tokyo, brings his metric tools over, and he tightened the bolt on the two battery terminals. I thought my problem was solved. Until about four days ago when there was no electrical connection, AND the banging on the battery cover didn't work. Has anyone else had this problem?
     
  2. SFO

    SFO Senior Member

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    What kind of voltage did you measure at the jump points under the hood ?

    Recheck all of the cabled connections in and around the 12v battery again, are the 3 wired connections also clipped in and secure?

    Disconnect and or look for rust where the negative ground cable connects to the body of the vehicle, sand and reattach if needed.

    Since you didn't list a location in your profile, we will assume that you might be in the Puget sound area. Maybe @PriusCamper can help.
     
  3. sam spade 2

    sam spade 2 Senior Member

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    THIS. It is also possible that there is a failed connection INSIDE the battery itself.
    Some simple voltage testing is needed.
     
  4. rjparker

    rjparker Senior Member

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    If it is an Optima battery its extremely likely the battery post has cracked. Poor quality.
     
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  5. RovinRon

    RovinRon Junior Member

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    Hmmm - by far no expert on cars whatsoever, however sounds similar to the problem I was having with our V 2 months back. Sometimes it wouldn't have any power when I attempted to start it, my wife's remote always worked when I went in and got it. Changed the battery in my remote and no problems. Have no idea why or if that was the problem, but so far so good!!
     
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  6. edthefox5

    edthefox5 Senior Member

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    measure the voltage across the 2 battery terminals. Write that down. Then measure the voltage at the front jump point.

    It should only be .5 volts lower at the front jump point.

    If it was me I would unbolt the negative wire where it bolts to the cars chassis. Sand down the mating area where the lug attaches.
    Sand down the lug mating area. Put some grease on that sanded area. Bolt it back up.

    Make sure the 2 black wires plugged into the terminal assy on top of the battery are plugged into there sockets. Push them in..

    Then do my test above.

    A healthy 12 volt battery in a Prius G2 should live at 12.6 volts at the front jump point. if lower than that test it.
    With car off turn off turn on the headlights in high beam. While the lights are on and car off measure the front jump point. It should not sag more than .3 volts with the highs on. I bet your battery tanks under this test like 11.5 volts.
     
  7. sam spade 2

    sam spade 2 Senior Member

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    Wrong order.
    That kind of a flat, smooth conductive surface should NEVER have plain or dielectric grease put on it BEFORE tightening it down.
    The grease is applied AFTER.
     
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