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Battery voltage gauge seems inconsistant

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by jeremyc, Sep 26, 2012.

  1. j cat

    j cat Rockstar 4 Years 1000 Posts

    I have checked into this voltage issue. the PCM turns OFF the alternator when in the fuel saving mode. this is not at all good for the battery . the constant charge / discharge will shorten the batteries life . GM however can claim that these vehicles get XXX MPG.

    Another reason for ME to not buy these vehicles.
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Over charging the battery is even worse for it, and whether you know it or not your present truck allows the battery to charge and discharge in the same manner only it uses the voltage regulator to do this instead of freewheeling the alternator. Doing the same thing only in a different manner and making the engine more efficient.
  3. dpeter

    dpeter Rockstar 3 Years 100 Posts

    Nothing is free. The fuel you save while not charging will HAVE to be spent on the extra power used to recharge. They get to claim fuel savings in that mode and I am sure they do but you can't stay there forever and when you come out of it, extra fuel wil be used to drive an alternator under a heavier load while recharging.
    Seems a poor choice to stress alternator and battery for PR and have the customer still pay for the gas and replace components prematurely. I would love to see the test data that proves me wrong.
  4. j cat

    j cat Rockstar 4 Years 1000 Posts

    I agree with this 100% ! your stressing out both the battery and alternator.

    The regulator over many decades now has been controlling the battery charging quite well.

    I get 7 years on my batteries. then replace. working or not.
  5. WorthFlorida

    WorthFlorida Member 2 Years 100 Posts

    I'm sure the alternator is working correctly. The defective battery was charged for 90 minutes and then load tested. The electrical system had to also be tested to be sure that the battery was getting a charge. GM builds 9 million vehicles a year, that is a lot of batteries and to get a bad one out of the box is quite probable. The heat in South Florida really beats up the lead acid batteries. If you get five years from any battery you're lucky. I've lived in South Florida for 22 years and of all the cars and trucks I've own an average of three-four years is normal. I've not have paid a full price on a battery for years. I buy the six year warranty units and they always get prorated.
  6. billnorman

    billnorman Rockstar 100 Posts

    What you're seeing is "normal". I watched mine and it seemed to only charge at 12 volts. Took it back to the dealer he told me it was OK. Two days later the battery went dead. They fixed something it now has 100,000 miles on it and reads higher than 13v most of the time.
  7. WorthFlorida

    WorthFlorida Member 2 Years 100 Posts

    The most common ways that a lead acid battery dies,

    1) The electron flow between the lead and lead oxide plate diminishes because the lead–acid batteries lose the ability to accept a charge due to sulfation, the crystallization of lead sulfate. This is more common in the northern states.

    2) The plates short out. When your gauge read ~12volts and a new battery it went back to 15 volts, the old battery was overloading the alternator with an internal short. At one time I had a battery short bring it down to 9 volts and the computer went nuts. The engine back fired I just made it to a battery shop. This is very common in the hot southern states. You can be starting the car all day long and then one time, completely dead, no warning. Only one time in the last 22 years living in South Florida that I was able to tell the OEM battery in our Highlander was going down. The cranking power was way down and it was five years old.

    http://en.wikipedia.org/wiki/Lead_acid_battery
    Last edited by a moderator: Aug 20, 2014

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