Batteries can supply electrical energy. The capacity of a battery is measured in amp-hours – symbol is Ah. Rechargeable and non-rechargeable batteries (UD260 , UD264 , UD265 )have different advantages and disadvantages. Technology continues to improve, providing us with faster, smaller and more useful electrical devices.

Battery capacity
The ability of a battery to supply electrical energy is called its capacity. The capacity of a battery is measured in amp-hours. This unit has the symbol Ah. You might also see battery capacity shown in milliamp-hours – mAh, especially on rechargeable batteries for mobile phones.

Here is the equation for working out a battery’s capacity:

capacity = current supplied × length of time supplied

So, a battery that can supply 2 amps for 4 hours has a capacity of 2 × 4 = 8 Ah.

How long can a battery last?
It is helpful to know how long a given battery should be able to supply electrical energy for. To do so, we re-arrange the equation above like this:

length of time supplied = capacity ÷ current supplied

There are two main types of battery: non-rechargeable batteries and rechargeable batteries.

Non-rechargeable batteries

Ordinary ‘dry-cell’ batteries are non-rechargeable. As the reactants inside them become used up in chemical reactions, the output from these batteries gradually falls. Once all the reactants have been used up, these batteries go ‘flat’ and cannot supply electrical energy anymore.

Rechargeable batteries

Rechargeable batteries 312-0279 , 312-0383 , 312-0386  usually maintain a constant output until just before they go flat. They contain reactants that can be made again just by passing electricity through the products. Once the battery has gone flat, it can be connected to a recharger. This uses electrical energy to reverse the chemical reactions that happened in the battery while it was in use.

Car batteries are rechargeable batteries – they are constantly recharged while the car is moving, so the lights and horn will always work.

Mobile phones, many MP3 players and other portable devices use rechargeable batteries. They must be recharged at regular intervals. It is usually recommended that such batteries should almost be flat before recharging. This allows the battery to be fully charged again.

Improving technology

Technology has improved over time. These are some of the devices that have improved during the last few decades:

• rechargeable batteries – smaller, higher capacity, faster recharge times
• microprocessors or computer chips – smaller and faster
• computer memory chips and disk drives – smaller, faster, higher capacity

All these devices have also become cheaper as a result of improvements such as these:

• computers have become small enough to carry around, instead of occupying a whole room
• mobile phones have reduced in size and weight, remain on for longer and have more features
• many household appliances are controlled by microprocessors
• new devices have been invented, including digital cameras and MP3 players