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What are correct Battery Voltages COLD??

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  • What are correct Battery Voltages COLD??

    After having some trouble with my dual battery system, I decided to get a Multimeter.
    This morning before starting the car I tested each battery for voltage. The starter battery showed 12.12v and the auxiliary battery showed 12.57v. How are those voltages?? Are they in the range where they should be? The car has been used each day and not standing for a long time.
    [color=#fa0c23][b]
    Brian
    [/b][/color]

    [color=#004080][b]2011 Silver GXL Diesel Auto with dual batteries & pirellis etc often pulling a Jayco Discovery Outback
    [/b][/color]

  • #2
    HI,

    Depends on SOC, temperature and age of your batteries.

    Your aux looks fine, cranking battery is a little low.

    If you do a search of the internet for battery terminal voltage versus state of charge
    of a lead acid battery you will find graphs showing how much charge is in your battery.

    In your case aux is around 100% charged, cranking battery around 40%.

    Cheers

    LeighW
    HKB Electronics, manufacturer of the Alternator Voltage Booster, Silver 2008 D4D,Lifted,Underbody protection, Alternator Voltage Booster, Tiger Z winch, Lightforce DL, Air Horns, Tanami Drawers, Drop down fridge slide, Outback cargo barriers, Rotronics dual Battery system, Polaris GPS, HF/UHF/VHF, Radio speaker combiner, Long ranger water tank, Diff breathers, Inverter, Snorkel and others

    Comment


    • #3
      Thanks Leigh. The aux battery is new but the starter battery is nearly 3 years old and the temp this morning was about 15C.
      [color=#fa0c23][b]
      Brian
      [/b][/color]

      [color=#004080][b]2011 Silver GXL Diesel Auto with dual batteries & pirellis etc often pulling a Jayco Discovery Outback
      [/b][/color]

      Comment


      • #4
        it all depends on when the vehicle was lasted used and how much charge it last received.
        if the vehicle was driven well the previous day, then i'd agree the starter battery is getting low.
        do you have a big amp battery charger? if so give it 24hrs of hard charge.
        it might come back or be no different.
        15' degrees in the morning? not what other might can a cold morning. try 3' degrees, or missus.
        either way, to test batteries properly, there are a few options.
        load tester (but this is risky as if your battery is low, it probably wont survive the test and need new battery there and then)
        or a battery acid test syringe type device, which tests the specific gravity of each cell/acid.
        we are now in the battery season. as anyone who has already just replaced there battery/batteries would know.
        with a sudden cold snap, any battery that was just hanging in there will quickly die.
        try pouring boiling water over battery, as this increases internal battery temp, and you may get another crank out of it,
        or the battery is just done for. replace battery time and probably at the worst time.
        (sorry got a little off topic)
        [url=http://www.fuelly.com/driver/damonat/prado][img]http://www.fuelly.com/smallsig-metric/50578.png[/img][/url]

        Comment


        • #5
          Hi Brian, this is a bit long winded and as above, there can be a number of factors that will effect your findings but, the cranking battery is a little easier to get a fairly accurate indication as to it’s SoC because there is always a load on this battery, even a very, VERY small load but this helps to keep the voltage at a settled level.

          Your auxiliary battery is another thing, the voltage on this battery can settle up a fair bit if there is no load on it.

          Your cranking battery is around the 50 to 55% SoC but your auxiliary battery could be anything from 50 to 90%.

          If you haven’t been using your auxiliary battery and it has just been charging as you drive around then there is every likely hood that your auxiliary battery, even with the higher voltage reading, is at about the same SoC as your cranking battery.

          This is because your cranking battery voltage reading is based on that of a loaded battery, and your auxiliary battery would have an “open circuit” voltage which is always a higher voltage reading than a loaded voltage reading for the same SoC.

          And as confusing as this all sounds, there is no easy way to get accurate SoC indications when using a voltage reading.

          No matter what type of battery you have, if it has a small load on it for a short period of time, like a fridge running while your camping, then the chart below will give you a fair indication of the state of charge of your auxiliary battery.

          You can use the same chart for your cranking battery at any time, but it is not that easy to get an accurate indication of any battery that is in an “open Circuit” state, like your auxiliary battery is. There are open circuit voltage charts but for these to be accurate, you need to have your auxiliary battery sit for at least 24 for hours in a No Load / No Charge state and even then there can be large variants in the voltage readings.

          Comment


          • #6
            Originally posted by Sunshine View Post
            After having some trouble with my dual battery system, I decided to get a Multimeter.
            It's best if you stated what your trouble was so as to get a better informed opinion.

            Cheers
            [SIZE=1]Cheers Jim.
            [/SIZE][COLOR=#0000cd]
            2009 120 D4D VX auto, pearl white with [COLOR=#0000cd]matching ARB deluxe bar,[/COLOR] 2" lift with [COLOR=#0000cd]OME springs & Nitro shocks,[/COLOR] 9000lb Warn winch, BFG KO A/Ts, Alloy Rhino roof basket, Safari snorkel, 2 x Optima D27F batteries, Voltage booster from Leigh, Jawa [SIZE=1]off-road camper trailer.[/SIZE][/COLOR]

            Comment

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