A D battery (D cell or IEC R20) is a standardized size of a dry cell. A D cell is cylindrical with an electrical contact at each end; the positive end has a nub or bump. D cells are typically used in high current drain applications, such as in large flashlights, radio receivers, and transmitters, and other devices that require an extended running time. A D cell may be either rechargeable or non-rechargeable. Its terminal voltage and capacity depend upon its cell chemistry.
The National Carbon Company introduced the first D cell in 1898. Before smaller cells became more common, D cells were widely known as flashlight batteries. The U.S. military designation for this battery has been BA-30 since sometime before World War II. During World War II, it was designated the Type C battery by the U.S. Navy, leading to confusion with the smaller C cell battery (BA-42).
In 2007, D batteries accounted for 8% of alkaline primary battery sales (numerically) in the US. In 2008, Swiss purchases of D batteries amounted to 3.4% of primary and 1.4% of secondary (rechargeable) sales.
D batteries have a nominal diameter of 33.2 ± 1 millimeters (1.3 inches).
The overall length is 61.5 millimeters (2.42 inches).
A battery’s capacity depends upon its cell chemistry and current draw. Duracell brand rates its alkaline D cell performance as approximately 20,000 mAh at 25 mA draw, but about 10,000 mAh at 500 mA draw. This effect is generally less pronounced in cells with NiMH chemistry and hardly at all with NiCd. Many commonly available size D rechargeable cells are actually sub-C cells in a D-sized holder.