A D battery (D cell or IEC R20) is a size of dry cell. A D cell is cylindrical with electrical contacts at each end; the positive end having 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 requiring extended run time. Rechargeable and non rechargeable cells are made in the D cell size, with terminal voltage and capacity varying depending on the 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 type since before WW II is BA-30.
As of 2007, D batteries accounted for 8% of alkaline primary battery sales in the US. In Switzerland as of 2008, D batteries totalled 3.4% of primary battery sales and 1.4% of secondary battery sales.
Dimensions and capacity
|Typical capacity||8000 mAh||12000-18000 mAh||2000-5500 mAh||2200–12000 mAh|
|Nominal voltage||1.5 V||1.5 V||1.5 V||1.25 V||1.25 V|
|Rechargeable||no||Special type only||No||Yes||Yes|
Capacity varies depending on cell chemistry and current draw, Energizer rates their alkaline D cell at approximately 20,000mAh at 25mA draw, but closer to 10,000mAh at 500mA draw. This effect is generally less pronounced in NiCd and NiMH chemistries; see Peukert's law. Many commonly available size D rechargeable cells are actually sub-C cells in a D-sized holder.
D batteries have:
Nominal diameter of 33.2 ± 1 millimeters (1.3 inches).
Overall length of 61.5 millimeters (2.42 inches). 
Other common names
- HP2 / SP2 / U2 (In Britain until the 1980s)
- Flashlight Battery
- Torcia (Italy)
- Type 373 (Soviet Union/Russia)
- BA-30 (US Military Spec WWII–1980s)
- UM 1 (JIS)
- #1 (China)
- 6135-99-464-1938 (NSN)(carbon-zinc)
- 6135-99-109-9428 (NSN)(alkaline)
- Pila Grande (Argentina)
- Brand Neutral Drawing Of Alkaline D Battery Based On ANSI Specifications
- Brand Neutral Drawing Of NiCd D Battery Based On ANSI Specifications
- Brand Neutral Drawing Of NiMH D Battery Based On ANSI Specifications
- Energizer D Size Battery Specification for Alkaline Cell
- Duracell D Size Battery Specification