The principal of modern lead acid batteries was discovered in the laboratory by the French physicist, Mr. Gaston Plante in 1860. Using pure lead plates and dilute sulfuric acid as an electrolyte he was able to charge the plates and then measure a current when discharging them through a load. Twenty years later Mr. Henri Tudor, a Luxembourg Engineer, started manufacturing lead acid batteries using pure lead Plante plates for the positive plate and a pasted negative plate.

The lead acid battery has been changed and improved many times over the years but the electrode reaction in all lead acid batteries is basically the same regardless of design or construction. As the battery is discharged the lead dioxide positive active material and the sponge lead negative material both react with the dilute sulfuric acid electrolyte to form lead sulphate and water, during charging this process is reversed.

The efficiency of the charge / discharge process is less than 100% because during the charge process the voltage has to be increased (over the discharge voltage) by about 7 to 10% to overcome chemical inefficiency and the cells internal resistance.

Over the years many different alloys of lead have been used to reduce the high cost of manufacturing the pure lead Plante plates.

Antimony lead alloy was first used, with up to 9% alloyed with pure lead, this caused the cell to gas freely and increased the current needed to charge the batteries. In later designs, the antimony was reduced to less then 2% to reduce the maintenance interval, in example, the intervals between the need to add distilled or de-ionized water.

In the 1960s calcium was alloyed with lead, this resulted in longer cell life, reduced load current requirements and reduced the need to add water to the cell, i.e. reduce the maintenance interval. In the early 1980's sealed valve regulated VRLA batteries were developed for use in telecommunications applications.

It has been shown that in vented / flooded electrolyte cells the positive electrode in a lead acid battery accepts charging less efficiently then the negative plate. Under typical charging conditions oxygen evolution at the positive plate peaks at a charge ampere hour / discharge ampere hour ratio of approximately 0.94, whereas the rate of hydrogen evolution at the negative plate reaches a maximum at a charge amp hour / discharge amp hour ration of 1:0.

This feature is used in the design of sealed valve regulated cells which oversize the negative plate to design a 'positive limited' cell, thus reducing the overall gas evolution, i.e. limiting the hydrogen evolution. Gas evolution was further reduced in sealed valve regulated cells by using antimony free lead alloys with reduced gassing rates and immobilized electrolyte either gelled or absorbed.

Thus today there are three main types of vented / flooded batteries : (1) the pure Plante lead plate, (2) the flat pasted plate and (3) the tubular positive plate and flat pasted negative plate batteries. Battery types (2) and (3) are commercially available in either antimony or calcium lead alloys.

The Plante positive plate batteries can provide long life but at a relatively high expense, the flat pasted plate and tubular plate cells are therefore commercially the most popular today.

With the vented / flooded batteries there is the presence of hydrogen and oxygen thus batteries must be housed in well vented, preferably air conditioned, battery rooms. Maintenance / cleaning or corroded terminals and the frequent addition of water to the cells adds to the battery total maintenance costs. This maintenance can be greatly reduced by the use of gas recombining caps which reduce the vented gas and thus maintenance by up to 75%. However, the now well established sealed valve regulated VRLA batteries are becoming the industry norm due to their considerable cost saving features:

1. They do not need to be put in special battery rooms as they do not gas appreciably in normal service, thus they can be placed in battery racks or cabinets or be placed free standing in the equipment room.
   
   
2. They are spill-proof and leak-proof therefore the maintenance to terminals and intercell interconnects is minimal
   
   
3. They generate less hydrogen gas, when properly charged and used, and are a safer product.
   
   
4. They are much more compact in design, saving up to 75% of the present floor space requirements.
   
   
5. Due to high production levels the cost of sealed valve regulated batteries is about the same as the installed cost of vented/flooded batteries.