The basic electrochemical reaction equation in a lead-acid battery can be written as follows: Pb + 2H2SO4 + PbO2 <---- Charging + PbSO4 + 2H2O + PbSO4 Discharging----> Or, in words: porous lead + sulfuric acid + porous lead dioxide active material electrolyte active material negative plate positive plate ^ charging ^ Becomes ---------------- V discharging V lead sulfate + water + lead sulfate active material electrolyte active material negative plate positive plate
This is how things work when the battery is new and clean. There are several effects that come in as the battery is used. One is the process called sulfation, which is of central concern to this effort. Here is Richard Perez, from Home Power magazine #29, page 44:
The biggest problem in lead-acid cells is sulfation due to chronic undercharging. Here the sulfate ions have entered into deep bonds with the lead on the cell's plates. The sulfate ions can bond with the lead at three successively deeper energy levels. Level One is the bond we use when we normally charge and discharge the cell. After a month or so at Level One, some of the bonds form Level Two bonds which require more electric power to break. After several months of being at Level Two bond, the sulfate ions really cozy up to the lead and form Level Three bonds. Level Three bonds are not accessible electrically. No amount of recharging will break Level Three bonds. The longer the lead sulfate bond stays at a level the more likely it is to form a closer acquaintance and enter the next deeper level. This is why it is so important to fully, regularly, and completely, recharge lead-acid cells.In the above, the Level One, Two, or Three bonds refer to progressively larger and insoluable crystals of lead sulfate. Like most crystal formation, it is a slow process. So the question is, How could pulse charging affect this situation? According to conventional wisdom, not at all. Here is the party line, from a product applications manager at Trojan Battery Co. on pulsing:
If the loss in capacity is due to Level Two bonding, then a repeated series of equalizing charges will break the Level Two bonds. Under equalization the Level Two bonds will first be transformed into Level One bonds, and then the sulfate ion can be kicked loose of the lead entirely and reenter the electrolyte solution. If your lead-acid cells have lost capacity, then a regime of equalizing charges is the first procedure to try. An equalization charge is a controlled overcharge of an already fully recharged cell. First recharge the cell and then continue to charge the cell at a C/20 rate for five to seven hours. During equalization charges, the cell voltage will become very high, about 2.7 VDC per cell. This overcharge contains the necessary power to break the Level Two bonds and force them to Level One. Once they reach Level One, the bond is easily broken and the sulfate ions reenter into solution in the electrolyte.
The active material in the positive electrode....is lead dioxide. This molecule is a relative of rust, it is a corrosion product. When you charge a lead acid battery, one of the things you attempt to accomplish is the repair or reformation of the corrosion layer of the positive plate. If you don't properly charge the battery, the corrosion layer begins to break down in the acid environment and the voltage characteristic of the battery changes for the worse.
Pulse charging does not influence or improve the corrosion layer of the positive electrode and therefore, does not permanently or properly improve the performance of the battery. It is only through the electrochemical process of corroding the positive electrode that you optimize the battery's performance. To properly corrode the positive electrode the battery voltage has to reach and then excced the gassing potential of the battery. In a deep cycle battery, not gassing the cells will result in stratified electrolyte, ineffective corrosion of the positive plate, reduced performance and shortened life.
My opinions on the matter, subject to further learning are: