Rechargeable Batteries

Rechargeable batteries

Rechargeable batteries, also known as accumulators or storage batteries, are types of electrical battery composed of one or more electrochemical cells. A rechargeable battery builds up or accumulates energy and is described as a secondary cell because it is possible to electrically reverse its electrochemical reactions. A primary cell is a battery that cannot be used after it has been discharged. Rechargeable batteries are available in a number of different forms and have a range of applications, including in smaller items such as cameras and torches as well as on a larger scale in cars and in megawatt systems, such as power stations and electrical distribution networks.


A brief history

In 1749, Benjamin Franklin first used the term "battery" when describing a set of linked capacitors used by him, for experiments with electricity. Fifty years later Italian physicist Count Alessandro Volta discovered the electrochemical reaction process, having created a simple battery from brine-soaked cardboard or paper and metal plates. Since then, scientists have greatly improved upon Volta's original design to create batteries made from a variety of materials that come in a multitude of sizes.

During the following 100 years various scientists developed different kinds of energy storage devices, often giving their name to the new cells in the process. Gaston Planté, in 1859, invented the first rechargeable battery by passing a reverse current through a lead-acid battery. A lead-acid cell comprises a lead dioxide cathode immersed in sulphuric acid and a lead anode. Lead sulphate is produced when the electrodes react with the acid, with the lead anode releasing electrons, which the lead dioxide duly consumes. In this way a current is produced, and Planté discovered that he could recharge the battery if he passed a reverse current through it because the chemical reactions would then be reversed.

Until the end of the 20th century, batteries continued to be made using many different materials, including nickel cadmium (NiCd), lithium ion (Li-ion), nickel metal hydride (NiMH) and lithium ion polymer (Li-ion polymer) as well as lead-acid. The first lithium ion battery prototype appeared in 1985, and was a rechargeable version of the lithium battery and was much more stable. Sony commercialised the lithium ion battery in 1991. Then, in 1997, the lithium ion polymer battery became the prime choice for portable electronics such as mobile phones and palmtop computers as a result of its flexibility and high energy density. Ten years later Stanford University’s Department of Materials Science and Engineering developed the nanowire battery, at about the same time as a paper-thin, flexible self-rechargeable battery appeared, combining an extremely thin and highly flexible lithium-polymer battery with a thin-film organic solar cell. This battery recharged itself when exposed to light.

The latest developments in rechargeable batteries are focusing on the potential of sodium-sulphur and lithium-sulphur as low-cost solutions that have low environmental impact and which scientists claim have four times the storage capacity of lithium-ion batteries.


Car battery charger

Rechargeable batteries for cars are usually referred to as SLI batteries – for the starter, lighting and ignition system of the engine. Some vehicles use a different type of battery, for example certain models of Porsche use a lithium-ion battery and since 2008 advances in battery technology has led to a renaissance in interest in electric cars, which can be powered at home and, in some places, via a network of recharging stations. Car batteries normally recharge themselves when a vehicle is being driven, however, sometimes when there is a vehicle fault a battery is drained and a car battery charger is needed.

The latest types of smart car battery chargers have the capacity to monitor progress and vary the current to prevent damage. They can also take their power from a mains socket and supply sufficient charge in a matter of minutes. The best types of car battery charger have more than one mode and can be used to top up car batteries as well as completely recharge them. It is also possible to use emergency power packs that can recharge a flat battery through the 12-volt socket inside a car. Read more about the car battery charger.


Solar battery charger

A solar battery charger works by converting sunlight energy into direct current (DC), an electric current that flows in one direction only, unlike alternating current (AC), which periodically reverses direction. Usually portable, a solar battery charger can also be fixed, for example as with solar panels. Often, solar panels are connected to an electrical grid, whereas portable solar chargers tend to be used off the grid, for example in boats, cars or caravans and other recreational vehicles, such as mobile homes.

Many portable solar chargers obtain energy only from the sun although some can be used in low light, that is, when it is cloudy, depending on the technology. Typically, portable solar chargers are used for what is known as trickle charging, which means enabling the battery to remain at its fully charged level by charging it at the same rate as it is self-discharging. There are some solar chargers that can recharge batteries completely, depending on the wattage. Read more about the solar battery charger.


Rechargeable AA batteries

Battery sizes vary considerably and they are differently labelled in different parts of the world. In the UK, rechargeable AA batteries are 14.5mm in diameter and 50.5mm long. Among the first available rechargeable batteries were Nickel Cadmium (NiCd) ones, however, they are fast disappearing as they have relatively low capacity and the heavy metal cadmium is due to be banned from use in consumer equipment within the next couple of years, because of its adverse impact on the environment.

The current most powerful, economical and easily available rechargeable batteries are Nickel Metal Hydride (NiMH) ones and these have become extremely popular, particularly amongst fans of digital photography. They have up to three times the capacity of the older NiCd version and outperform Alkaline batteries in high drain applications by a factor of 10. A set of four rechargeable AA batteries costs just a few pounds and they can be charged very quickly. Read more about rechargeable AA batteries.


Camera batteries

A set of rechargeable camera batteries for a digital camera is a great asset, specifically NiMH AA ones. They are reasonably inexpensive and will provide hundreds of charges before requiring replacement. This is a cheaper and a more environmentally friendly option than constantly buying sets of disposable batteries. NiMH batteries with a capacity of at least 2000mAh will yield maximum life and the higher the rating, the more power capacity there is. Generally, the maximum capacity of a rechargeable AA NiMH battery is circa 2850mAh.

In the long term, to maximize the overall life of rechargeable camera batteries, it is best to let them drain completely after a photography session before recharging. There are many manufacturers that now recommend Lithium ion (Li-ion) AA batteries, which certainly have a high power capacity. For more information on the best AA camera batteries, read the additional information.


Important technical elements

SLI batteries, the type generally used in vehicles, are normally of the lead-acid type, made up of six galvanic cells in series that provide a 12-volt system. Each cell delivers 2.1 volts for a total of 12.6 volts when the battery is fully charged. Heavy vehicles such as large lorries or tractors are often equipped with diesel engines and may have two batteries in series, creating a 24-volt system, or they may have parallel strings of batteries instead.

Solar battery chargers employ solar energy to charge batteries and are generally portable. They can charge lead acid, or a Ni-Cd battery, back up to a capacity of hundreds of ampere-hours (for example, up to 400 Ah) and 48 volts. Usually ‘intelligent’ charge controllers are used, comprising a series of solar cell array plates that are installed separately on, for example, a rooftop, whichcan be connected to a bank of batteries. This type of arrangement can also be used alongside mains supply chargers to enable energy saving during the daytime.

A rechargeable AA battery is composed of a single electrochemical cell, the exact terminal voltage, and capacity of which, depends on the cell chemistry. Rechargeable AA batteries are available in multiple forms: nickel–cadmium (NiCd) with a capacity of 500–1100 mAh; nickel–metal hydride (NiMH) with capacities that vary between 1300–2700 mAh; and, lithium-ion – this last has a nominal voltage of 3.6 volts and is referred to as a 14500 li-ion battery. More than 50 per cent of battery sales worldwide are for AA batteries.

As digital cameras have shrunk over time, so the need for smaller, but more powerful batteries has grown. The most common rechargeable batteries are AA, both disposable and rechargeable varieties, however AAA batteries, CR2 and CR-V3 batteries are also used in some cameras. Both CR2 and CR-V3 batteries are lithium based, and intended for single use only, therefore are not rechargeable. In addition, there are proprietary batteries that are built to a manufacturer’s custom specifications. Practically all of the available proprietary batteries are lithium ion.


How batteries work: a scientific illustration

Essentially, batteries provide a mobile source of power that makes it possible to enjoy many modern conveniences. They work by storing energy generated by electricity.

Electricity is the flow of electrons through a conductive path called a circuit. Often this path is a wire. When an electrical circuit is hooked up to a battery, it activates three separate elements. These are: an anode, denoted as (-); a cathode, denoted as (+); and, the electrolyte. Chemical reactions in the battery cause electrons to build up at the anode. There is, therefore, an electrical difference between the cathode and the anode and the electrons attempt to rearrange themselves by heading for the cathode via the circuit (wire) activating any connected item, such as a light bulb, along the way. However, in a battery the electrochemical processes change the chemicals in the cathode and anode to limit the supply of electrons, thus the supply of power in a battery is also limited.

When recharging a battery, the direction of the flow of electrons using another power source, such as solar panels, is changed. The electrochemical processes therefore happen in reverse, and the cathode and anode are restored to their original state and have the capacity, once again, to provide full power.


The manufacturing perspective

The national trade association for the portable battery industry for the UK and Ireland is the British Battery Manufacturers Association (BBMA). In terms of UK and European regulations, the European Batteries Directive is a recent set of guidelines that aims to improve the environmental performance of accumulators and batteries and minimise their environmental impact. One of the key ways this can be accomplished is via the setting up of collection and recycling targets for portable batteries waste.

On 5 May 2009, the UK regulations transposing these requirements into UK law came into force and introduced an important series of new measures, which included assigning responsibility to the manufacturer of batteries for battery collection and recycling as well as introducing collection targets of 25 per cent to be reached by 2012 and 45 per cent to be reached by 2016.

The BBMA continues to engage with stakeholders and with government within the industry to ensure that all manufacturers work together to ensure that targets are met and that consumers are aware of the recycling options available to them.

From February 2010, there are new obligations pertaining to distributors who supply 32kg or more of portable batteries per annum to an individual store, or via distance sales, for example, via internet, mail order or telesales. These distributors will have new obligations under the Batteries Regulations, which include providing collection facilities for used batteries.

In the UK, there are six battery compliance schemes (BCSs) that are responsible for the collection, treatment and recycling of batteries on behalf of large manufacturers, that is, those producers placing more than one tonne of portable batteries on the UK market every year.