Lead sulfation actually starts when you remove the charging voltage from a fully charged lead-acid battery. Though the lead sulfate crystals are converted back to lead during the normal charging cycle, the real question is, if all of the lead sulfate crystals are not turned back into lead, how long does it take before they become so hard that they can not be converted?

The answer is that varies–it could be weeks or months and depends on a number of factors such as the quality of the lead, temperature, plate chemistry, porosity, Depth-of-Discharge (DoD), electrolyte stratification, and so on.

During the normal discharge process, lead and sulfur combine into soft lead sulfate crystals are formed in the pores and on the surfaces of the positive and negative plates inside a lead-acid battery. When a battery is left in a discharged condition, continually undercharged, or the electrolyte level is below the top of the plates or stratified, some of the soft lead sulfate re-crystallizes into hard lead sulfate. It cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called permanent or hard “sulfation”. When it is present, the battery shows a higher voltage than it’s true voltage; thus, fooling the voltage regulator into thinking that the battery is fully charged. This causes the charger to prematurely lower it’s output voltage or current, leaving the battery undercharged.

Sulfation accounts for approximately 84% of the lead-acid battery failures that are not used at least once per week. The longer sulfation occurs, the larger and harder the lead sulfate crystals become. The positive plates will be light brown and the negative plates will be dull, off white. These crystals lessen a battery’s capacity and ability to be recharged. This is because deep cycle and some starting batteries are typically used for short periods, vacations, weekend trips, etc., and then are stored the rest of the year to slowly self-discharge. Starting batteries are normally used several times a month, so sulfation rarely becomes a problem unless they are undercharged or the plates are not covered with electrolyte.

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I purchased two 24v desulfators for our wind/solar farm about three months ago. Battery condition was so poor the desulfators weren't always operating and the LEDs didn't come on very often.

After slowly recharging the system for the last three months the desulfators are working most of the time now as our battery capacity increases. Overall capacity is 2,360 Amp Hours!, so this has been a really big job!

These desulfators are making a big difference for our battery investment. Specific gravity is also increasing. Yesterday we had 24 hours of 60 kph (35mph) winds and finally reached equalizing voltages for the first time in a year, and maxed out at 29.9v a few times.

Solar panels charge 22 to 28 amps to the batteries at 24V in full sunlight. Four windmills charge 70 amps in gusty conditions. Prior to adding the desulfators, quiescent battery voltages were 23.4 to 23.8 volts.

After attaching the desulfators for two months the batteries now average 24.2 to 24.8 volts. More power is supplied to the inverter and voltage drops are not as sharp. Capacity appears to be increasing as the desulfators do their work. These eight batteries (318 lbs. each) are made by Surette in Nova Scotia and are fondly termed "submarine batteries". I am convinced that desulfators are essential equipment for wind/solar powered homes."