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AGM Deep Cycle Battery Question.

Discussion in 'Home Power and Microgeneration' started by Richard P., Feb 18, 2005.

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  1. Richard P.

    Richard P. Guest

    Can anyone point the way toward some information regarding the care of AGM type deep cycle
    batteries? I have been gifted some Interstate 12v units and I am normally used to testing battery
    state of health by measuring the specific gravity of the cells. Naturally I can't do it with these

    Also, can AGM's be stored outside (protected from the elements, of course) and handle cold weather
    without damage..?? Although I am in a mild climate area, it does get down several degrees below
    zero centigrade at night.

    Thanks for any info...!
  2. Vaughn Simon

    Vaughn Simon Guest

    It may not be too scientific, but I have made it through the last ten
    years by checking the state of charge with a voltmeter, and testing the
    internal impedance of the battery with an ordinary automotive-type load
    tester. I am responsible for about 100 batteries and I have never felt the
    need for anything better. I have found that a charged battery that will not
    pass the load test is a bad battery, exactly like on your car.
    Read the manufacturer's literature, but a doubt if a few degrees below
    freezing is likely to be a problem, particularly if you keep the batteries

  3. Me

    Me Guest

    You might want to look at the manuals for the Absolyte II Series of AGM
    batteries from GNB Industrial Power. These are what the BIG Boys are
    using for Remote Site Battery Power, these days.

  4. The only way you can tell the state of charge is the terminal voltage when
    the battery is at rest. Get the manufacturer's chart.

    AGM batteries cannot be destroyed by freezing.
    However, these batteries will not fulfill the specified lifetime unless the
    charger compensates with a thermal probe that measures the temperature of a
    The problem with outside storage is that the daily range of temperature is
    so large that the temperature measured by the probe on the surface of the
    battery will never accurately reflect the internal temperature, which is
    what matter. Therefore the battery will be alternately undercharged and
    overcharged. During overcharge, the battery loses water that cannot be

    The neat thing about AGMs is that you can place them inside without fear of
    acid damage. Consider doing this.
  5. The following may be helpful:

    Specific Gravity = Cell Open Circuit Voltage - 0.845

    with voltages taken after 30 minutes or more of
    resting (no charging or discharging).
    Bill Kaszeta
    Photovoltaic Resources Int'l
    Tempe Arizona USA
  6. That would be for a flooded battery.
    In an AGM battery, the electrolyte is semi-solid.
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