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 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).
Dimensions and capacity
|Typical capacity||charge||8000 mAh||12000-18000 mAh||2000-5500 mAh||2200–12000 mAh|
|energy||12 Wh||18-27 Wh||2.5-6.9 Wh||2.75-15 Wh|
|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|
A battery's capacity depends upon its cell chemistry and current draw. Energizer brand rates its alkaline D cell at approximately 20,000mAh at 25mA draw, but estimates performance closer to about 10,000mAh at 500mA draw. This effect is generally less pronounced in cells with 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
- "U.S. Army Flashlight".
- Life Cycle Impacts of Alkaline Batteries with a Focus on End-of-Life - EPBA-EU Archived 7 October 2011 at the Wayback Machine
- "Absatzzahlen 2008" (PDF). Archived from the original (PDF) on 25 March 2012. Retrieved 25 March 2012. INOBAT 2008 statistics.
- "MN1300 Size: D (LR20) Alkaline-Manganese Dioxide Battery" (PDF). Archived from the original (PDF) on 21 May 2012.
- IEC 60086-2 §7.1.4
- Duracell D Size Battery Specification
- Energizer D Size Battery Specification for Alkaline Cell
- Brand Neutral Drawing Of NiCd D Battery Based On ANSI Specifications
- Brand Neutral Drawing Of NiMH D Battery Based On ANSI Specifications
- Brand Neutral Drawing Of Alkaline D Battery Based On ANSI Specifications