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.
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
- Cadmium sulphate additive and charging at high voltage.
Magnesium sulphate replacement of electrolyte followed by charging and then replacement with fresh electrolyte.
Application of a high frequency AC voltage to the battery.
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.