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Testing Your Battery For Sulfation


The following, if done correctly, will tell you more about the condition of your battery than any "anecdotal" history ever would. Use a digital voltmeter and a temperature compensated (Floating Ball type or Gauge type) hydrometer for the testing, and a BatteryMINDer charger  maintainer to avoid future problems with battery sulfation.

Testing a 12 Volt or 24 Volt Filler Cap Lead Acid Battery

  • Carefully remove all filler caps from your battery.
  • Check the water-liquid electrolyte level.
    • If the level is low or has ever been below top of plates, severe lead plate sulfation has taken place.  Significant recharge/reconditioning time is needed to restore these plates to a condition where the battery may be expected to function normally.
  • Refill each cell with distilled water only to the liquid level indicator found in each cell.  Before proceeding further you must be thoroughly familiar with the safety and operating instructions.
  • Recharge the battery with the BatteryMINDer battery charger desulfator to ensure that it is slowly and completely charged before you determine its condition.
  • Allow battery to "REST" overnight for a minimum of 12 hours.
  • Test the battery with a temperature compensated hydrometer and/or digital type voltmeter only.  See the sections on Testing with a Temperature Compenstated Hydometer Tester and Digital Voltmeter below for more information.
  • Your battery may be too far gone to be fully desulfated if one of the following conditions occurs:
      • BatteryMINDer battery condition LED lights (YELLOW) within 72 hours (single battery)
      • Gauge reading is 1.120 or no balls float on the hydometer in one or more cells,.  See the Specific Gravity - Capacity chart below for more information.
  • Reconnect battery to your BatteryMINDer battery charger desulfator.
  • Allow battery to remain in maintenance mode for a minimum of 72 hours, before re-test.
    • Use a temperature compensated hydrometer tester for the most accurate results (see table).
    • If you see an increase in the Specific Gravity (SG) or voltage indicating that there is an improvement in the battery's condition, continue desulfating for an additional 72 hours and retest the battery.
    • Continue this process until the SG or voltage readings no longer increase.

Testing with a Temperature Compensated Hydrometer Tester

  • Read the tester instructions carefully for most accurate readings.
  • Use caution when testing Specific Gravity (SG) with a hydrometer.  If not done properly, acid can spill, which can burn skin or clothing.
  • When using the tester the first time or after a long period of non-use, fill the tester with the battery fluid and let it sit for 1/2 hour or longer.  This will soak the balls in the hydrometer in order to give you more accurate readings.  Failure to do so will give you false readings indicating a battery that may not be in as good a condition as you may have thought.
  • After inserting the tester in a cell, gently tap the tester several times against the inside wall of each cell to dislodge air bubbles that will cause more balls to float than should.  Failure to do so will yield false readings that indicate a battery that is not fully desulfated or does not qualify for desulfation.
  • If no balls float in any cell, the cell is shorted.  This means your battery is beyond the point of being properly recharged or reconditioned-desulfated.  Dispose of the battery.
  • If each cell floats three (3) or more balls (or 1250 on gauge-type), your battery can be reconditioned-desulfated.
  • Always rinse the tester with fresh water after every use.  Failure to do so will cause false readings.
Specific Gravity - Capacity
Temperature Compensated Hydrometer (Gauge type or Floating Ball type ) Full Capacity Percentage
1.270 (4 Balls floating) 100%
1.250 (3 Balls floating) 75%
1.190 (2 Balls floating) 50%
1.150 (1 Balls floating) 25%
1.120 (0 Balls floating) May denote shorted cell or battery that has been severely discharged and may not be recoverable 0%

Testing a Sealed, AGM or Flooded (Wet-cell) Lead Acid Battery Use a Digital Voltmeter Only

    These batteries have no filler caps or manifold-type covers.  Because you cannot gain access to the interior of your battery you cannot test it with a hydrometer. 

  • Recharge the battery with the BatteryMINDer battery charger desulfator to ensure it is as completely charged as possible, before you determine its condition.
  • Allow battery to "REST" overnight before checking the open circuit voltage with a digital voltmeter only.  Failure to check a "RESTED" battery will cause false readings.  Be certain to read and understand all safety related instructions contained in your BatteryMINDer manual before proceeding further.
  • Measure battery's voltage, without any load attached.
    • If the voltage is less than 12.4 volts (for a 12 volt battery) or 24.8 volts (for a 24 volt battery), which is typically 75% of charge,  the battery may be too heavily sulfated to be fully recoverable.
    • If voltage is 12.4 volts (for a 12 volt battery) or 24.8 volts (for a 24 volt battery) or higher recovery can be expected, given sufficient time.
  • Connect the BatteryMINDer to the battery.
  • Charge battery to its maximum level.
  • Allow battery to remain for a minimum of 72 hours before retesting.
    • If improvement is seen, continue until battery voltage reaches full capacity level or no further increase is seen.

Note: Do not expect to completely dissolve sulfate in a day.  Long established sulfate will require a longer period to be fully dissolved.  Be patient and you will rewarded with a "sulfate-free" battery.