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Lead Acid Battery Facts

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  • Lead Acid Battery Facts

    As charging circuits have evolved it is time to understand what
    the newer excepted perimeters are for charging a lead acid battery.

    Three Stage Battery Charging

    The BULK stage involves about 80% of the recharge, wherein the
    charger current is held constant (in a constant current charger), and
    voltage increases. The properly sized charger will give the battery as
    much current as it will accept up to charger capacity
    (25% of battery capacity in amp hours), and not raise a wet battery over 125 F, or
    an AGM or GEL (valve regulated) battery over 100 F.

    The ABSORPTION stage (the remaining 20%, approximately) has the
    charger holding the voltage at the charger's absorption voltage
    (between 14.1 VDC and 14.8 VDC, depending on charger set points)
    and decreasing the current until the battery is fully charged. Some
    charger manufacturers call this absorption stage an equalization
    stage. We don't agree with this use of the term. If the battery
    won't hold a charge, or the current does not drop after the
    expected recharge time, the battery may have some permanent

    The FLOAT stage is where the charge voltage is reduced to between
    13.0 VDC and 13.8 VDC and held constant, while the current is reduced
    to less than 1% of battery capacity. This mode can be used to maintain
    a fully charged battery indefinitely.

    Recharge time can be approximated by dividing the amp hours to be
    replaced by 90% of the rated output of the charger. For example, a
    100 amp hour battery with a 10 % discharge would need 10 amps
    replaced. Using a 5 amp charger, we have 10 amp hours divided by
    90% of 5 amps (.9x5) amps = 2.22 hour recharge time estimate.
    A deeply discharged battery deviates from this formula, requiring
    more time per amp to be replaced.

    Recharge frequency recommendations vary from expert to expert.
    It appears that depth of discharge affects battery life more than
    frequency of recharge. For example, recharging when the equipment
    is not going to be used for a while (meal break or whatever), may
    keep the average depth of discharge above 50% for a service day.
    This basically applies to battery applications where the average
    depth of discharge falls below 50% in a day, and the battery can
    be fully recharged once during a 24 hour period.

  • #2
    Battery Testing

    Battery Testing

    Battery testing can be done in several ways. The most popular
    includes measurement of specific gravity, and battery voltage.
    Specific gravity applies to wet cells with removable caps, giving access
    to the electrolyte. To measure specific gravity, buy a temperature
    compensating hydrometer at an auto parts store or tool supply.
    To measure voltage, use a digital voltmeter in the DC voltage
    setting. The surface charge must be removed from a freshly
    charged battery before testing. A 12 hour lapse after charging
    qualifies, or you may remove the surface charge with a load (20
    amps for 3 plus minutes).

    State of Charge Voltage Specific Gravity

    12V 6V
    100% 12.7 6.3 1.265
    75% 12.4 6.2 1.225
    50% 12.2 6.1 1.190
    25% 12.0 6.0 1.155
    Discharged 11.9 6.0 1.120

    Load testing is another method of testing a battery. Load testing
    removes amps from a battery (similar to starting an engine). Some
    battery companies label their battery with the amp load for testing.
    This number is usually 1/2 of the CCA rating. For instance, a 500
    CCA battery would load test at 250 amps for 15 seconds. A load
    test can only be performed if the battery is at or near a full charge.
    Some electronic load testers apply a 100 amp load for 10 seconds,
    and then display battery voltage. This number is compared to a
    chart on the tester, based on CCA rating to determine battery

    Sulphation of batteries starts when specific gravity falls below
    1.225 or voltage measures less than 12.4 (12v Battery ) or 6.2
    (6 volt battery). Sulphation can harden on the battery plates if
    left long enough, reducing and eventually destroying the ability of
    the battery to generate rated volts and amps. There are devices for
    removing hard sulphation, but the best practice is preventing
    formation by proper battery care and recharging after a discharge
    cycle. Sulphation is the main reason a significant portion of lead
    acid batteries don't attain their chemical life span.


    • #3
      a very useful resource for beginners and professionals

      many of the fellows use this resource

      Battery Information Table of Contents, Basic to Advanced
      If you want to Change the world
      BE that change !!


      • #4
        Scooter Battery Charge Rates

        At this site find what a slow charge is for a 5ah battery made with
        lead plates.

        standard rate charger:

        12 Volt 1 Amp slow charge

        12 Volt 2 Amp fast rate charge

        12 Volt 5-8 Ah Pack

        However very few sites talk about minimum charging rates because
        taking to long to charge is bad for batteries unless you have pulsing

        The new switchmode charging circuitry is counted in these days and
        considered an improvement.

        Last edited by BroMikey; 11-07-2017, 11:59 PM.