D
Direct Answer
A D battery (IEC designation LR20, ANSI 13A) measures 34.2mm in diameter and 61.5mm in length -- the largest common cylindrical primary cell. Alkaline D cells output 1.5V nominal, with typical capacity in the range of roughly 12,000 to 20,000 mAh depending on discharge rate.
Source: IEC 60086-2
Specs
| Diameter | 34.20 mm |
| Length | 61.50 mm |
| Alkaline Voltage | 1.50 V |
The Largest Standard Cylindrical Cell
The D battery is the largest of the standard cylindrical primary cell sizes still in wide production, built to the same IEC 60086-2 alkaline standard as AA, AAA, and C but with substantially more internal volume than a C cell. That extra volume gives D cells the highest sustained-current capability in the family, which is why they remain the standard choice for large flashlights, lanterns, and battery-powered radios designed for extended outdoor or emergency use.
Like other alkaline cylindrical cells, the D cell follows the LR20 code under IEC 60086-2, with a corresponding 1.2V NiMH rechargeable version (HR20) sharing the identical 34.2mm x 61.5mm envelope.
Emergency and High-Drain Use
D cells are a mainstay of emergency-preparedness kits precisely because of their combination of long shelf life (typically a decade or more for alkaline chemistry) and high sustained capacity, which matters for devices like battery-powered weather radios and large flashlights that may need to run continuously for hours during a power outage. Multi-cell D battery packs also historically powered items like boomboxes and early portable electronics before rechargeable lithium-ion packs became standard, though D cells remain in production today mainly for these high-drain, infrequent-use scenarios rather than everyday portable electronics.