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Battery voltage issue

Discussion in 'Gen 2 Prius Technical Discussion' started by ThePackage, May 21, 2009.

  1. ThePackage

    ThePackage New Member

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    I have been using ScanGage for several years and monitor battery voltage as one of my set points. Over this long period, the voltage shows as 13.8 which I have accepted as standard. When the system is off (the last few seconds after shutting the Prius off), the voltage reads at 12.2 volts with no load and 11.5 with the head lights on. Again, I've accepted this as normal. Just today, I was driving, with out head lights, and the voltage reading was a consistent 13.2 volts. I turned my headlight on while driving and the voltage shot back up to 13.8. I turned the lights off and the voltage went back to 13.2. I repeated this action several more time with the same results. When I returned home I checked the voltage at shut down and it was the same as noted above.

    Can anyone shed any light on this? Is this a pre-cursor to the 12 volt battery going bad or is it something with the inverter or inverter control? My car is an '06 with 50K on it and no prior electrical problems. Please HELP.
     
    #1 ThePackage, May 21, 2009
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    What's the ambient temp outside when you noticed the measurement of 13.2V?

    Although I've only seen 13.8V on the DC bus when the car is READY, I've seen some posters say that the voltage may drop down to 13.2V if the 12V battery is fully charged. Perhaps this is happening in your case.

    I wouldn't worry about this yet, if the voltage doesn't drop below 13.2 and you don't see any warning lights appear. The skid control ECU is especially quick to turn on the BRAKE and VSC warning lights if it doesn't like the voltage on the 12V bus.
     
    #2 Patrick Wong, May 21, 2009
  3. David Beale

    David Beale Senior Member

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    Curious. The only change from 13.8 I've seen is when I leave my amateur radio on when the car is off for an hour or three ;). Then the voltage goes -UP-, as in 13.9 or even (gasp) 14.0. So a "low" battery should result in a higher charge voltage. It may indeed be "fully charged" or it may be at end of life (sulfate on plates) and not providing much "load" on the charging circuit, causing it to drop the voltage. You might want to load test the battery, but don't let a mechanic hook up a starter battery load tester! Max. load of about 50A with a voltage output around 11.0 would indicate a good battery. If it drops to 10.0 you've sulphated at least one cell and it's time to replace.
     
    #3 David Beale, May 21, 2009
  4. hschuck

    hschuck Member

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    I experience a similar, but somewhat different, battery voltage variation. (Using an original scangauge.)

    My battery voltage reads 13.5 when the car is operating with no driver added loads. With an added load (ventilation fan or A/C or headlights) the voltage jumps up to 14.0/14.1. This behavior was first noticed about a year ago and seems to be consistent after the warm-up cycle is complete. Initially it is at 14.0/14.1. Prior to noticing this behavior I almost always used auto a/c so I would not have seen it.

    Since my battery was over 4 years old my suspicion was that a failing battery was causing the noted behavior. I replaced my original battery a month ago with an Optma from LearnAid. The behavior is unchanged.

    It does not concern me anymore. Should it?
     
    #4 hschuck, May 21, 2009
  5. ThePackage

    ThePackage New Member

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    Thank you all for the info. The outside air temp, here is NJ, is now about 70F. I am hoping to get at least 4 years out of the 12V battery so that leaves about 10 mos. to go. Since I am not currently getting any "error" codes, I'll keep monitoring and let PC know if there are any changes. Thanks again.
     
    #5 ThePackage, May 22, 2009
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    This seems OK.

    Makes good sense; you may want to replace the battery before next winter as a preventive move if you would be unduly inconvenienced by a no-start situation. Good luck.
     
    #6 Patrick Wong, May 22, 2009
  7. Cacti

    Cacti Poleikleng

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    I too had this question in a recent post, here's the link:http://priuschat.com/forums/care-ma...ng/60877-12-volt-battery-operation-range.html
     
    #7 Cacti, May 22, 2009
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