A D battery is a cylindrical battery commonly used in various devices that require a significant amount of power. It typically measures about 61.5 mm in length and 34.2 mm in diameter. D batteries are often used in flashlights, portable radios, and toys due to their long-lasting energy supply. These batteries come in different types, including alkaline, lithium, and rechargeable options. The alkaline battery is the most common type, known for its reliability and shelf life. D batteries are part of the standard battery sizes defined by the International Electrotechnical Commission (IEC) and are designated as size 1.5V.