A D battery (D cell or IEC R20) is a size of 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, boomboxes, products with electric motors, safety systems, Geiger counters, megaphones, or other applications 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 WWII.
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 sales.