A battery stores electricity to power electrical devices, in this case cordless power tools such as cordless drill drivers.
A battery only lasts a certain length of time before all the energy is used up. The battery is either a ‘primary’ battery which means it cannot be recharged and must be recycled; or it is a ‘secondary’ battery or ‘rechargeable’ battery which means the energy inside the battery can be restored. This guide is only concerned with rechargeable batteries suitable for use in cordless power tools.
There are three types of rechargeable battery used for cordless power tools: Nickel cadmium (NiCd, pronounced “nye-cad”), nickel metal hydride (NiMH, usually just referred to as ‘metal hydride’) and lithium ion (Li-ion, pronounced ‘lye eye-on’) batteries.
A rechargeable battery can be recharged using a charger. The charger passes modified electricity from the mains power through the battery and ‘resets’ it so it is ready to work again.
Cordless power tools often come in a set with one or two batteries and a compatible charger, although cordless power tools can often be bought as a ‘bare unit’ without battery or charger, which are then purchased separately.