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Lead-Acid Batteries
The first rechargeable battery was the lead-acid cell invented in 1859 by French physicist Gaston Planté. Lead-acid batteries work in a similar way to Volta’s original invention, but use electrodes of lead and lead dioxide in an electrolyte of sulphuric acid. This reaction has the advantage of being reversible, so that electrical energy can be stored in the cell.

This type of battery is still in use today, primarily in vehicles, where its ability to provide very high surge currents is useful for powering starter motors. However in some respects lead-acid batteries have even greater disadvantages than voltaic cells, in that they are even heavier and therefore not suited to portable applications, and their components are highly toxic and difficult to dispose of safely.

The key concept in the development of portable rechargeable batteries is that of energy density, in other words the amount of electrical energy that can be stored in a give mass and volume. Lead acid batteries have relatively poor energy density for their mass, so work continued to find a better type of rechargeable battery.

Nickel-Cadmium
In 1899 Swedish scientist Waldemar Jungner created the first Nickel-Cadmium battery, which after some development came to have significantly higher energy density than lead-acid types, and these went into commercial production by 1906. Development has continued, and Nickel-Cadmium (NiCd, or commonly “Nicad”) rechargeable batteries are still in use today, most commonly in radio-controlled models and other specialist applications.

They have a number of advantages over more modern alternatives. They provide a constant voltage as they discharge; they can be used for longer, typically 3000 charge cycles; they hold a charge in storage longer, and are capable of high surge current output. They can also be stored for long periods in a discharged state. However they have a few disadvantages too, the primary concern being that Cadmium is extremely toxic, leading to problems of disposal and recycling. They are also said to suffer from something called the “memory effect”.

Supposedly, if a NiCd battery is repeatedly partially discharged to the same point and then fully recharged, it develops a “memory” of the discharge point, and will subsequently suffer a voltage drop at this point, appearing to be fully discharged while still holding a partial charge. There is some disagreement over the extent of this problem, but it is one of the reasons that NiCd batteries have become less popular in recent years, replaced by more modern alternatives.

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