Lead Acid Battery Tutorial

- lead acid batteries are widely used in many applications, and they have become particularly widely used for automotive applications.

Lead acid batteries have been in existence for many years. They are able to provide a relatively high current level and their technology is well established and widely available.

Another reason for the widespread use of lead acid batteries is that they are cheap and they can be easily manufactured with relatively low technology equipment.

The batteries are used in many applications, but one of the most visible is within cars where they are able to supply the current required for many tasks including starting, where their high surge capability is ideal. In addition to this, lead acid batteries are used in many other applications where they may provide main or auxiliary power.


Lead acid battery history

The lead acid battery was the first form of rechargeable battery to be developed. The idea was originally proposed by a French Physicist named Gaston Plante in 1860.

Although another French scientist named Gautherot had discovered that platinum or silver wires that had been used to electrolyse saline water produced a current for a short duration, this was never developed into a workable battery.

The first lead acid cells were made from lead plates. The battery then had to be 'formed' by charging it so that one of the plates oxidised. The battery then increased its capacity over successive charge discharge cycles.

Plante's basic cell was later improved by a further French engineer named Faure. He managed to make the forming process much shorter by using some strips of lead oxide onto the plates. This speeded up the forming process considerably as the negative plate became lead only, and the positive plate oxidised to become lead peroxide.

Once the basic lead acid battery technology was established, the next major development involved addressing the problem that existed of water loss and the electrolyte drying up. Batteries needed period topping up with distilled water in order to ensure their operation. This was overcome by inserting a valve into the battery. These valve-regulated lead-acid batteries, VRLA by utilising an oxygen recombination mechanism. The gases produced inside VRLA battery are made to recombine inside and the battery which is sealed under normal conditions.


Lead acid battery basics

A lead acid battery cell has comparatively few components. Essentially it consists of four main elements:

  • Positive plate:   This is covered with a paste of lead dioxide.
  • Negative plate:   This is made of sponge lead.
  • Separator:   This is an insulating material between the two plates, but it allows the electrolyte and the ions into it to enable conduction without the two plates touching.
  • Electrolyte:   This consists of water and sulphuric acid

These constituents are all contained within a plastic container which acts to keep the electrolyte in and the battery together.

The overall battery will consist of several cells placed in series to give the required voltage as each cell is capable of providing an EMF of 2.1 volts.

Basic lead acid cell diagram
Diagram of the concept behind a lead acid rechargeable cell

In order to enable the basic lead acid cell to produce a voltage, it must first receive charge. The voltage applied to provide this must be greater than the 2.1 volts to enable current to flow into the cell. If it were less than this, charge would actually flow out of it.

Once charged, the cell or battery will be able to provide charge to external circuits, often operating over several hours dependent upon the drain on the cell or battery.


Lead acid battery advantages & disadvantages

Although lead acid batteries are widely used because they have a number of distinct advantages, they also have several major disadvantages. All these need to be considered when deciding upon whether to use this technology or not.

Lead Acid Battery Advantages & Disadvantages
Advantages
  • Mature technology
  • Relatively cheap to manufacture and buy (they provide the lowest cost per unit capacity for rechargeable cells)
  • Large current capability
  • Can be made for a variety of applications
  • Tolerant to abuse
  • Tolerant of overcharging
  • Wide range of sizes and specifications available
  • Many producers worldwide
Disadvantages
  • Fails after a few years use lifespan typically 300 - 500 cycles
  • Cannot always be used in a variety of orientations
  • Corrosive electrolyte (can cause burns to people and corrosion on metalwork)
  • Lead is not environmentally friendly
  • Acid needs disposing of with care
  • Not suitable for fast charging
  • Must be stored in charged state once electrolyte introduced
  • Typical charging efficiency only around 70%

Although there are many disadvantages to its use, the lead acid battery has gained a significant foothold in its use. As it has been available for over 150 years, and because of its high current capability, cost and tolerance to abuse, the battery is currently the only viable option for many applications. However with other battery technologies developing, it is likely that its use will reduce in the years to come.

By Ian Poole

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