Simple question, complicated answer.
I will try to answer as succinctly as possible.
Sulphate crystal build up has been known about since the Lead Acid battery was first invented, and this build up leads to over 70% of premature failure of lead acid batteries. However all
wear out over time and no device can stop that happening.
Over the last 30 years or so battery manufactures have made great strides in combatting sulphate build up and improving the life span of their batteries, by introducing changes to the construction of the battery plates, and in ideal circumstances, proper maintenance and correct charging, sulfation should not be a problem.
However we do not live in a perfect world and sulphate build up remains the major cause of battery failure.
It has been found that a controlled overcharge of the battery will break down the crystals, and if used correctly will keep the batteries in good clean condition, and extend the useful life of the battery. This method is not recommended to be used on sealed lead acid batteries (also known as AGM or VRLA batteries)
Around 20 years ago a simple device that created high voltage pulse sent to the battery was developed, called a pulse generator or desulfator. This, in practice, created the same effect as the controlled overcharge except it was not regulated, so over time these high voltage pulses damaged the battery plates. This negated the positive effect. The circuit board diagrams for this type of device are freely available on the internet and many of the low-cost devices available today are built using these designs. Short-term solution, long-term damage.
At the same time alternative solution were considered and experimentation showed that if a frequency pulse was sent to the battery it could break down the sulphate build up if the correct frequency could be achieved, however different frequencies were required for different sizes of crystal that built up on the plates. So the devices using the single frequency method were and still are, hit and miss, some work some worthless.
What was needed was a device that would work over a range of frequencies, voltages and size of battery. Until the last few years building this type of device was very expensive (in excess of $1,000) and large (the size of an old style video player). As no guarantee could be given to the end-user that sulfation was the problem with their battery no companies were prepared to develop them.
Dramatic drops in the size and cost of components has allowed companies to produce small reasonable prices products able to clean the plates of batteries of various capacities and voltages.
A small number of manufactures around the world now produce products that can clean the plates of old batteries and stop the sulphate build-up on new batteries, so recovering them or keeping new batteries clear of the build-up. In effect recovering many old batteries and extend the life of any battery that is not charged or maintained in the correct way. This is ALL they do and is the only thing responsible manufactures claim that their desulfators can do, they cannot recover batteries with any internal damage, shorted cells or AGM batteries that have dried out.
As it is not possible for suppliers to determine the condition or faults of the batteries customers intend to use the device on you should look for suppliers, who give clear information of how to test for faults within the battery, or offer a telephone or email service to help with any problems you may have with using a desulfator or with your specific battery setup.
In conclusion modern multi frequency desulfators are not a magic bullet that will repair all faulty batteries, but they can significantly extend the life of your lead acid batteries, and recover a large proportion of batteries that are sulphated and would otherwise be scrapped. This would greatly reduce you replacement
costs, which is not insignificant on applications like solar storage batteries, ride on golf carts, fork trucks, large boats and motor homes.
This article is by Dan Hornby product development manager at Battery Extra Ltd. A leading manufacturer of battery management products.
The Battery Extra desulfator range covers lead acid batteries and battery banks from 12 to 120 volts and up to 3,000Ah in capacity. All carry a 60 day 100% refund guarantee and a 3 year warranty. This allows a user sufficient time to try our product and if it does not work for them to return it to us with no financial penalty.