Proposed Desulphation Techniques

A number of techniques for recovery of batteries have been suggested. Only three appear to have any reasonable scientific plausibility, although the chemistry and physics behind them are quite unclear.

  1. Cadmium sulphate additive and charging at high voltage.
  2. Magnesium sulphate replacement of electrolyte followed by charging and then replacement with fresh electrolyte.

  3. Application of a high frequency AC voltage to the battery.

A good start is a Battery University article on preventing sulphation. It is pointed out that sulphation can occur in various degrees depending on the way the battery has been treated, with early intervention likely to have much better success. Batteries that have been left on low charge for weeks or months may not respond as well. However for expensive batteries it may be worth making the attempt.

The key strategy behind these techniques appears to be that of encouraging a significant charging current to flow in order to chemically reduce the lead sulphate back to the original forms. A fully sulphated battery will have a high resistance and as such will hinder the flow of current.

A useful website with a good discussion of desulphation is Batteryvitamin. This is a commercial organisation offering additives for lead acid batteries. They provide a number of articles that give an in-depth and convincing discussion of sulphation processes and desulphation techniques. The articles also refer to experiments carried out over a number of years, and conclusions drawn from these. While these have not necessarily been carried out with full scientific rigour, they nevertheless provide valuable experience. Note I do not endorse any commercial product, but I do note the value of these articles.

There are many warnings about using these techniques as high voltage charging can result in excessive grid corrosion and the formation of short circuits. Also it is reiterated that many techniques that have been proposed have no reasonable scientific merit and may be little more than mythology.

Additives Plus High Voltage Charge

It has been suggested that adding a small amount of CdSO4 and charging at high voltage is a very effective way of reversing sulphation. The cadmium sulphate was obtained from a commercial battery additive. Its purpose seems to be to electroplate onto the plate surfaces and form a conductive layer that can allow a heavy charging current to flow.

Metallic Sulphate Electrolyte Replacement

This technique has been reported to be successful but the chemical basis behind it is not clear. It involves removing all electrolyte and replacing it with a solution of MgSO4. The battery is then charged, the MgSO4 removed and replaced with fresh electrolyte (the old electrolyte will have been somewhat depleted). The MgSO4 apparently interacts with the PbSO4 and causes it to break down during charging. Other substances that are cheaply and readily available are sodium and aluminium sulphates, but these may not necessarily be as effective.

An interesting paper has been made available by Sylph Dominic Hawkins (New Alternative Electrolytes for Flooded Lead Acid Batteries) in which he discusses the chemistry behind the use of metallic sulphates such as MgSO4 as an alternative electrolyte. He has also produced a paper (How can we De-sulphate Lead-Acid Batteries for re-use) that discusses desulphation, but is not publically available at this time.

High Frequency Current

This technique has appeared in a number of forms in patents and commercial products. It is often referred to as "pulsing". It has been reported as being successful but again the physics behind these proposals is not clear and is usually never explained. One suggestion that seems plausible is that the lead sulphate forms a dielectric layer. A high frequency alternating voltage applied to the terminals can then result in a substantial current flow. These currents would provide very rapid charge-discharge cycles that may assist in breaking down the lead sulphate crystals. This would benefit from some serious investigation to see it does actually have any value.

First created
30 October 2017
Last Modified 30 October 2017
Ken Sarkies 2017