Primary batteries; they generate energy in a process of irreversible chemical reactions. They are not rechargeable.

For NiCd and NiMH rechargeable batteries.

The most widely used source of independent light, providing a great variety of models.

Secondary batteries; the chemical reactions that produce their energy are reversible. When the terminals receive current, the reactions inside are inverted and the battery is being recharged.

Writeable CDs and DVDs - long term storage for music, films, software, etc.